The GNU Name System

Internet-Draft	The GNU Name System	October 2020
Schanzenbach, et al.	Expires 21 April 2021	[Page]

2. Zones

A zone in GNS is defined by a zone type "ztype" that identifies a cryptosystem and a public/private key pair "(d,zk)", where "d" is the private key and "zk" the corresponding public key in the public key cipher identified by the "ztype". The contents of a zone are cryptographically signed before being published a distributed hash table (DHT). Records are grouped by their label and encrypted (Section 6.3) using an encryption key derived from the label and the zone public key. Instead of the zone private key "d", the signature MUST be created using a blinded public/private key pair "d'" and "zk'". This blinding is realized using a hierarchical deterministic key derivation (HDKD) scheme. Such a scheme allows the deterministic derivation of keys from the original public and private zone keys using "label" values. Specifically, the zone owner can derive private keys "d'", and a resolver to derive the corresponding public keys "zk'". Using different "label" values in the derivation results in different keys. Without knowledge of the "label" values, the different derivations are unlinkable both to the original key and to each other. This prevents zone enumeration and requires knowledge of both "zk" and the "label" to confirm affiliation with a specific zone. At the same time, the blinded "zk'" provides nodes with the ability to verifiy the integrity of the published information without disclosing the originating zone.¶

The following variables are associated with a zone in GNS:¶

ztype: is the unique type of the zone type as registered in the GNUnet Assigned Numbers Authority [GANA]. The zone type determines which cryptosystem is used for the asymmetric and symmetric key operations of the zone. A 32-bit number.¶
d: is the private zone key. The specific format depends on the zone type.¶
zk: is the public zone key. The specific format depends on the zone type.¶
zid: is the unique public identifier of a zone. It consists of the "ztype" and the public zone key "zk".¶
zTLD: is a string which encodes the "ztype" as well as the zone key "zk" into a domain name. The "zTLD" is used as a globally unique reference to a specific namespace in the process of name resolution.¶

The "zid" wire format is defined as follows:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|       ZONE TYPE       |      PUBLIC ZONE KEY  /
+-----+-----+-----+-----+                       /
/                                               /
/                                               /

Figure 1

For the string representation of the "zid", we use a base-32 encoding "StringEncode". However, instead of following [RFC4648] we base our character map on the optical character recognition friendly proposal of Crockford [CrockfordB32]. The only difference to Crockford is that the letter "U" decodes to the same base-32 value as the letter "V" (27).¶

zkl := <StringEncode(zid)>

If "zkl" is less than 63 characters, it is also the "zTLD". If the resulting "zkl" should be longer than 63 characters, the string must be divided into smaller labels separated by the label separator ".". Here, the most significant bytes of the "zid" must be contained in the rightmost label of the resulting string and the least significant bytes in the leftmost label of the resulting string. For example, assuming a "zkl" of 130 characters, the encoding would be:¶

zTLD := zkl[126:129].zkl[63:125].zkl[0:62]

4. Resource Records

A GNS implementor MUST provide a mechanism to create and manage resource records for local zones. A local zone is established by selecting a zone type and creating a zone key pair. Implementations SHOULD select a secure zone type automatically and not leave the zone type selection to the user. Records may be added to each zone, hence a (local) persistency mechanism for resource records and zones must be provided. This local zone database is used by the GNS resolver implementation and to publish record information.¶

A GNS resource record holds the data of a specific record in a zone. The resource record format is defined as follows:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   EXPIRATION                  |
+-----+-----+-----+-----+-----+-----+-----+-----+
|       DATA SIZE       |          TYPE         |
+-----+-----+-----+-----+-----+-----+-----+-----+
|           FLAGS       |        DATA           /
+-----+-----+-----+-----+                       /
/                                               /
/                                               /

Figure 2

where:¶

EXPIRATION: denotes the absolute 64-bit expiration date of the record. In microseconds since midnight (0 hour), January 1, 1970 in network byte order.¶
DATA SIZE: denotes the 32-bit size of the DATA field in bytes and in network byte order.¶
TYPE: is the 32-bit resource record type. This type can be one of the GNS resource records as defined in Section 4 or a DNS record type as defined in [RFC1035] or any of the complementary standardized DNS resource record types. This value must be stored in network byte order. Note that values below 2^16 are reserved for allocation via IANA ([RFC6895]), while values above 2^16 are allocated by the GNUnet Assigned Numbers Authority [GANA].¶
FLAGS: is a 32-bit resource record flags field (see below).¶
DATA: the variable-length resource record data payload. The contents are defined by the respective type of the resource record.¶

Flags indicate metadata surrounding the resource record. A flag value of 0 indicates that all flags are unset. The following illustrates the flag distribution in the 32-bit flag value of a resource record:¶

... 5       4         3        2        1        0
------+--------+--------+--------+--------+--------+
/ ... | SHADOW | EXPREL | SUPPL  | PRIVATE|    /   |
------+--------+--------+--------+--------+--------+

Figure 3

where:¶

SHADOW: If this flag is set, this record should be ignored by resolvers unless all (other) records of the same record type have expired. Used to allow zone publishers to facilitate good performance when records change by allowing them to put future values of records into the DHT. This way, future values can propagate and may be cached before the transition becomes active.¶
EXPREL: The expiration time value of the record is a relative time (still in microseconds) and not an absolute time. This flag should never be encountered by a resolver for records obtained from the DHT, but might be present when a resolver looks up private records of a zone hosted locally.¶
SUPPL: This is a supplemental record. It is provided in addition to the other records. This flag indicates that this record is not explicitly managed alongside the other records under the respective name but may be useful for the application. This flag should only be encountered by a resolver for records obtained from the DHT.¶
PRIVATE: This is a private record of this peer and it should thus not be published in the DHT. Thus, this flag should never be encountered by a resolver for records obtained from the DHT. Private records should still be considered just like regular records when resolving labels in local zones.¶

5. Record Types

A registry of GNS Record Types is described in Section 12. The registration policy for this registry is "First Come First Served", as described in [RFC8126].¶

5.1. PKEY

In GNS, a delegation of a label to a zone of type "PKEY" is represented through a PKEY record. The PKEY number is a zone type and thus also implies the cryptosystem for the zone that is being delegated to. A PKEY resource record contains the public key of the zone to delegate to. A PKEY record MUST be the only record under a label. No other records are allowed. A PKEY DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   PUBLIC KEY                  |
|                                               |
|                                               |
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 4

where:¶

PUBLIC KEY: A 256-bit ECDSA zone key.¶

For PKEY zones the zone key material is derived using the curve parameters of the twisted edwards representation of Curve25519 [RFC7748] (a.k.a. edwards25519) with the ECDSA scheme ([RFC6979]). Consequently , we use the following naming convention for our cryptographic primitives for PKEY zones:¶

d: is a 256-bit ECDSA private zone key.¶
zk: is the ECDSA public zone key corresponding to d. It is defined in [RFC6979] as the curve point d*G where G is the group generator of the elliptic curve. The public key is used to uniquely identify a GNS zone and is referred to as the "zone key".¶
p: is the prime of edwards25519 as defined in [RFC7748], i.e. 2^255 - 19.¶
G: is the group generator (X(P),Y(P)) of edwards25519 as defined in [RFC7748].¶
L: is the prime-order subgroup of edwards25519 in [RFC7748].¶

The "zid" of a PKEY is 32 + 4 bytes in length. This means that a "zTLD" will always fit into a single label and does not need any further conversion.¶

Given a label, the output d' of the HDKD-Private(d,label) function for zone key blinding is calculated as follows for PKEY zones:¶

zk := d * G
PRK_h := HKDF-Extract ("key-derivation", zk)
h := HKDF-Expand (PRK_h, label | "gns", 512 / 8)
d' := h * d mod L

Equally, given a label, the output zk' of the HDKD-Public(zk,label) function is calculated as follows for PKEY zones:¶

PRK_h := HKDF-Extract ("key-derivation", zk)
h := HKDF-Expand (PRK_h, label | "gns", 512 / 8)
zk' := h mod L * zk

The PKEY cryptosystem uses a hash-based key derivation function (HKDF) as defined in [RFC5869], using HMAC-SHA512 for the extraction phase and HMAC-SHA256 for the expansion phase. "PRK_h" is key material retrieved using an HKDF using the string "key-derivation" as salt and the public zone key "zk" as initial keying material. "h" is the 512-bit HKDF expansion result. The expansion info input is a concatenation of the label and string "gns". "label" is a UTF-8 string under which the resource records are published.¶

We point out that the multiplication of "zk" with "h" is a point multiplication, while the multiplication of "d" with "h" is a scalar multiplication.¶

The Sign() and Verify() functions for PKEY zones are implemented using 512-bit ECDSA deterministic signatures as specified in [RFC6979].¶

The S-Encrypt() and S-Decrypt() functions use AES in counter mode as defined in [MODES] (CTR-AES-256):¶

RDATA := CTR-AES256(K, IV, BDATA)
BDATA := CTR-AES256(K, IV, RDATA)

The key "K" and counter "IV" are derived from the record "label" and the zone key "zk" as follows:¶

PRK_k := HKDF-Extract ("gns-aes-ctx-key", zk)
PRK_n := HKDF-Extract ("gns-aes-ctx-iv", zk)
K := HKDF-Expand (PRK_k, label, 256 / 8);
NONCE := HKDF-Expand (PRK_n, label, 32 / 8)

HKDF is a hash-based key derivation function as defined in [RFC5869]. Specifically, HMAC-SHA512 is used for the extraction phase and HMAC-SHA256 for the expansion phase. The output keying material is 32 octets (256 bits) for the symmetric key and 4 octets (32 bits) for the nonce. The symmetric key "K" is a 256-bit AES [RFC3826] key.¶

The nonce is combined with a 64-bit initialization vector and a 32-bit block counter as defined in [RFC3686]. The block counter begins with the value of 1, and it is incremented to generate subsequent portions of the key stream. The block counter is a 32-bit integer value in network byte order. The initialization vector is the expiration time of the resource record block in network byte order. The resulting counter ("IV") wire format is as follows:¶

0     8     16    24    32
+-----+-----+-----+-----+
|         NONCE         |
+-----+-----+-----+-----+
|       EXPIRATION      |
|                       |
+-----+-----+-----+-----+
|      BLOCK COUNTER    |
+-----+-----+-----+-----+

Figure 5

5.2. EDKEY

In GNS, a delegation of a label to a zone of type "EDKEY" is represented through a EDKEY record. The EDKEY number is a zone type and thus also implies the cryptosystem for the zone that is being delegated to. An EDKEY resource record contains the public key of the zone to delegate to. A EDKEY record MUST be the only record under a label. No other records are allowed. A EDKEY DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   PUBLIC KEY                  |
|                                               |
|                                               |
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 6

where:¶

PUBLIC KEY: A 256-bit EdDSA zone key.¶

For EDKEY zones the zone key material is derived using the curve parameters of the twisted edwards representation of Curve25519 [RFC7748] (a.k.a. edwards25519) with the Ed25519-SHA-512 scheme [ed25519]. Consequently , we use the following naming convention for our cryptographic primitives for EDKEY zones:¶

d: is a 256-bit EdDSA private zone key.¶
a: is is an integer derived from "d" using the SHA512 hash function as defined in [ed25519].¶
zk: is the EdDSA public zone key corresponding to "d". It is defined in [ed25519] as the curve point "a*G" where "G" is the group generator of the elliptic curve and "a" is an integer derived from "d" using the SHA512 hash function. The public key is used to uniquely identify a GNS zone and is referred to as the "zone key".¶
p: is the prime of edwards25519 as defined in [RFC7748], i.e. 2^255 - 19.¶
G: is the group generator (X(P),Y(P)) of edwards25519 as defined in [RFC7748].¶
L: is the prime-order subgroup of edwards25519 in [RFC7748].¶

The "zid" of an EDKEY is 32 + 4 bytes in length. This means that a "zTLD" will always fit into a single label and does not need any further conversion.¶

The "EDKEY" HDKD instantiation is based on [Tor224]. Given a label, the output of the HDKD-Private function for zone key blinding is calculated as follows for EDKEY zones:¶

zk := a * G
PRK_h := HKDF-Extract ("key-derivation", zk)
h := HKDF-Expand (PRK_h, label | "gns", 512 / 8)
h[31] &= 7
a1 := a / 8 /* 8 is the cofactor of Curve25519 */
a2 := h * a1 mod L
a' = a2 * 8 /* 8 is the cofactor of Curve25519 */

Equally, given a label, the output of the HDKD-Public function is calculated as follows for PKEY zones:¶

PRK_h := HKDF-Extract ("key-derivation", zk)
h := HKDF-Expand (PRK_h, label | "gns", 512 / 8)
h[31] &= 7  // Implies h mod L == h
zk' := h * zk

We note that implementors must employ a constant time scalar multiplication for the constructions above. Also, implementors must ensure that the private key "a" is an ed25519 private key and specifically that "a[0] & 7 == 0" holds.¶

The EDKEY cryptosystem uses a hash-based key derivation function (HKDF) as defined in [RFC5869], using HMAC-SHA512 for the extraction phase and HMAC-SHA256 for the expansion phase. "PRK_h" is key material retrieved using an HKDF using the string "key-derivation" as salt and the public zone key "zk" as initial keying material. "h" is the 512-bit HKDF expansion result. The expansion info input is a concatenation of the label and string "gns". The result of the HKDF must be clamped. "a" is the 256-bit integer corresponding to the 256-bit private zone key "d". "label" is a UTF-8 string under which the resource records are published.¶

We point out that the multiplication of "zk" with "h" is a point multiplication, while the division and multiplication of "a" and "a1" with the cofactor are integer operations.¶

Signatures for EDKEY zones using the derived private key "a'" are NOT compliant with [ed25519]. Instead, signatures MUST be generated as follows for any given message M and deterministic random-looking "r":¶

R := r * G
S := r + SHA512(R, zk', M) * a' mod L

A signature (R,S) is valid if the following holds:¶

SB == R + SHA512(R, zk', M) * A'

The S-Encrypt() and S-Decrypt() functions use AES in galois counter mode as defined in [GCM] (GCM-AES-256):¶

RDATA := GCM-AES-256(K, IV, BDATA)
BDATA := GCM-AES-256(K, IV, RDATA) = CIPHERTEXT | GCM_TAG

The result of the GCM encryption function is the encrypted ciphertext concatenated with the 128-bit GCM authentication tag "GCM_TAG". Accordingly, the length of BDATA equals the length of the RDATA plus the 16 octets of the authentication tag.¶

The key "K" and counter "IV" are derived from the record "label" and the zone key "zk" as follows:¶

PRK_k := HKDF-Extract ("gns-aes-ctx-key", zk)
PRK_n := HKDF-Extract ("gns-aes-ctx-iv", zk)
K := HKDF-Expand (PRK_k, label, 256 / 8);
IV := HKDF-Expand (PRK_n, label, 96 / 8)

HKDF is a hash-based key derivation function as defined in [RFC5869]. Specifically, HMAC-SHA512 is used for the extraction phase and HMAC-SHA256 for the expansion phase. The output keying material is 32 octets (256 bits) for the symmetric key and 12 octets (96 bits) for the IV. The symmetric key "K" is a 256-bit AES [RFC3826] key. No additional authenticated data (AAD) is used.¶

5.3. GNS2DNS

It is possible to delegate a label back into DNS through a GNS2DNS record. The resource record contains a DNS name for the resolver to continue with in DNS followed by a DNS server. Both names are in the format defined in [RFC1034] for DNS names. A GNS2DNS DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                    DNS NAME                   |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                 DNS SERVER NAME               |
/                                               /
/                                               /
|                                               |
+-----------------------------------------------+

Figure 7

where:¶

DNS NAME: The name to continue with in DNS (0-terminated).¶
DNS SERVER NAME: The DNS server to use. May be an IPv4/IPv6 address in dotted decimal form or a DNS name. It may also be a relative GNS name ending with a "+" top-level domain. The value is UTF-8 encoded (also for DNS names) and 0-terminated.¶

5.4. LEHO

Legacy hostname records can be used by applications that are expected to supply a DNS name on the application layer. The most common use case is HTTP virtual hosting, which as-is would not work with GNS names as those may not be globally unique. A LEHO resource record is expected to be found together in a single resource record with an IPv4 or IPv6 address. A LEHO DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                 LEGACY HOSTNAME               |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 8

where:¶

LEGACY HOSTNAME: A UTF-8 string (which is not 0-terminated) representing the legacy hostname.¶

NOTE: If an application uses a LEHO value in an HTTP request header (e.g. "Host:" header) it must be converted to a punycode representation [RFC5891].¶

5.5. NICK

Nickname records can be used by zone administrators to publish an indication on what label this zone prefers to be referred to. This is a suggestion to other zones what label to use when creating a delegation record (Section 3) containing this zone's public zone key. This record SHOULD only be stored under the empty label "@" but MAY be returned with record sets under any label as a supplemental record. Section 8.2.6 details how a resolver must process supplemental and non-supplemental NICK records. A NICK DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                  NICKNAME                     |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 9

where:¶

NICKNAME: A UTF-8 string (which is not 0-terminated) representing the preferred label of the zone. This string MUST NOT include a "." character.¶

5.6. BOX

In GNS, every "." in a name delegates to another zone, and GNS lookups are expected to return all of the required useful information in one record set. This is incompatible with the special labels used by DNS for SRV and TLSA records. Thus, GNS defines the BOX record format to box up SRV and TLSA records and include them in the record set of the label they are associated with. For example, a TLSA record for "_https._tcp.example.org" will be stored in the record set of "example.org" as a BOX record with service (SVC) 443 (https) and protocol (PROTO) 6 (tcp) and record TYPE "TLSA". For reference, see also [RFC2782]. A BOX DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|   PROTO   |    SVC    |       TYPE            |
+-----------+-----------------------------------+
|                 RECORD DATA                   |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 10

where:¶

PROTO: the 16-bit protocol number, e.g. 6 for tcp. In network byte order.¶
SVC: the 16-bit service value of the boxed record, i.e. the port number. In network byte order.¶
TYPE: is the 32-bit record type of the boxed record. In network byte order.¶
RECORD DATA: is a variable length field containing the "DATA" format of TYPE as defined for the respective TYPE in DNS.¶

5.7. VPN

A VPN DATA entry has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|          HOSTING PEER PUBLIC KEY              |
|                (256 bits)                     |
|                                               |
|                                               |
+-----------+-----------------------------------+
|   PROTO   |    SERVICE  NAME                  |
+-----------+                                   +
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 11

where:¶

HOSTING PEER PUBLIC KEY: is a 256-bit EdDSA public key identifying the peer hosting the service.¶
PROTO: the 16-bit protocol number, e.g. 6 for TCP. In network byte order.¶
SERVICE NAME: a shared secret used to identify the service at the hosting peer, used to derive the port number requird to connect to the service. The service name MUST be a 0-terminated UTF-8 string.¶

6. Publishing Records

GNS resource records are published in a distributed hash table (DHT). We assume that a DHT provides two functions: GET(key) and PUT(key,value). In GNS, resource records are grouped by their respective labels, encrypted and published together in a single resource records block (RRBLOCK) in the DHT under a key "q": PUT(q, RRBLOCK). The key "q" which is derived from the zone key "zk" and the respective "label" of the contained records.¶

6.1. DHT Key Derivations

Given a label, the DHT key "q" is derived as follows:¶

q := SHA512 (HDKD-Public(zk, label))

label: is a UTF-8 string under which the resource records are published.¶
zk: is the public zone key.¶
q: Is the 512-bit DHT key under which the resource records block is published. It is the SHA512 hash over the derived public zone key.¶

6.2. Resource Records Block

GNS records are grouped by their labels and published as a single block in the DHT. The grouped record sets MAY be paired with any number of supplemental records. Supplemental records must have the supplemental flag set (See Section 4). The contained resource records are encrypted using a symmetric encryption scheme. A GNS implementation must publish RRBLOCKs in accordance to the properties and recommendations of the underlying DHT. This may include a periodic refresh publication. A GNS RRBLOCK has the following format:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|       ZONE TYPE       |    PUBLIC ZONE KEY    |
+-----+-----+-----+-----+       (BLINDED)       |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   SIGNATURE                   |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+
|         SIZE          |       PURPOSE         |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   EXPIRATION                  |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                    BDATA                      /
/                                               /
/                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 12

where:¶

ZONE TYPE: is the 32-bit zone type.¶
ZONE PUBLIC KEY: is the blinded public zone key "HDKD-Public(zk, label)" to be used to verify SIGNATURE.¶
SIGNATURE: The signature is computed over the data following the PUBLIC KEY field. The signature is created using the Sign() function of the cryptosystem of the zone and the derived private key "HDKD-Private(d, label)" (see Section 3).¶
SIZE: A 32-bit value containing the length of the signed data following the PUBLIC KEY field in network byte order. This value always includes the length of the fields SIZE (4), PURPOSE (4) and EXPIRATION (8) in addition to the length of the BDATA. While a 32-bit value is used, implementations MAY refuse to publish blocks beyond a certain size significantly below 4 GB. However, a minimum block size of 62 kilobytes MUST be supported.¶
PURPOSE: A 32-bit signature purpose flag. This field MUST be 15 (in network byte order).¶
EXPIRATION: Specifies when the RRBLOCK expires and the encrypted block SHOULD be removed from the DHT and caches as it is likely stale. However, applications MAY continue to use non-expired individual records until they expire. The value MUST be set to the expiration time of the resource record contained within this block with the smallest expiration time. If a records block includes shadow records, then the maximum expiration time of all shadow records with matching type and the expiration times of the non-shadow records is considered. This is a 64-bit absolute date in microseconds since midnight (0 hour), January 1, 1970 in network byte order.¶
BDATA: The encrypted resource records with a total size of SIZE - 16.¶

6.3. Record Data Encryption and Decryption

A symmetric encryption scheme is used to encrypt the resource records set RDATA into the BDATA field of a GNS RRBLOCK. The wire format of the RDATA looks as follows:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|     RR COUNT          |        EXPIRA-        /
+-----+-----+-----+-----+-----+-----+-----+-----+
/         -TION         |       DATA SIZE       |
+-----+-----+-----+-----+-----+-----+-----+-----+
|         TYPE          |          FLAGS        |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                      DATA                     /
/                                               /
/                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   EXPIRATION                  |
+-----+-----+-----+-----+-----+-----+-----+-----+
|       DATA SIZE       |          TYPE         |
+-----+-----+-----+-----+-----+-----+-----+-----+
|           FLAGS       |        DATA           /
+-----+-----+-----+-----+                       /
/                       +-----------------------/
/                       |                       /
+-----------------------+                       /
/                     PADDING                   /
/                                               /

Figure 13

where:¶

RR COUNT: A 32-bit value containing the number of variable-length resource records which are following after this field in network byte order.¶
EXPIRATION, DATA SIZE, TYPE, FLAGS and DATA: These fields were defined in the resource record format in Section 4. There MUST be a total of RR COUNT of these resource records present.¶
PADDING: The padding MUST contain the value 0 in all octets. The padding MUST ensure that the size of the RDATA WITHOUT the RR COUNT field is a power of two. As a special exception, record sets with (only) a zone delegation record type are never padded. Note that a record set with a delegation record MUST NOT contain other records.¶

8. Name Resolution

Names in GNS are resolved by recursively querying the DHT record storage. In the following, we define how resolution is initiated and each iteration in the resolution is processed.¶

GNS resolution of a name must start in a given starting zone indicated using a zone public key. Details on how the starting zone may be determined is discussed in Section 10.¶

When GNS name resolution is requested, a desired record type MAY be provided by the client. The GNS resolver will use the desired record type to guide processing, for example by providing conversion of VPN records to A or AAAA records, if that is desired. However, filtering of record sets according to the required record types MUST still be done by the client after the resource record set is retrieved.¶

8.1. Recursion

In each step of the recursive name resolution, there is an authoritative zone zk and a name to resolve. The name may be empty. Initially, the authoritative zone is the start zone. If the name is empty, it is interpreted as the apex label "@".¶

From here, the following steps are recursively executed, in order:¶

Extract the right-most label from the name to look up.¶
Calculate q using the label and zk as defined in Section 6.1.¶
Perform a DHT query GET(q) to retrieve the RRBLOCK.¶
Verify and process the RRBLOCK and decrypt the BDATA contained in it as defined in Section 6.3.¶

Upon receiving the RRBLOCK from the DHT, apart from verifying the provided signature, the resolver MUST check that the authoritative zone key was used to sign the record: The derived zone key "h*zk" MUST match the public key provided in the RRBLOCK, otherwise the RRBLOCK MUST be ignored and the DHT lookup GET(q) MUST continue.¶

8.2. Record Processing

Record processing occurs at the end of a single recursion. We assume that the RRBLOCK has been cryptographically verified and decrypted. At this point, we must first determine if we have received a valid record set in the context of the name we are trying to resolve:¶

Case 1: If the remainder of the name to resolve is empty and the record set does not consist of a delegation, CNAME or DNS2GNS record, the record set is the result and the recursion is concluded.¶
Case 2: If the name to be resolved is of the format "_SERVICE._PROTO" and the record set contains one or more matching BOX records, the records in the BOX records are the result and the recusion is concluded (Section 8.2.4).¶
Case 3: If the remainder of the name to resolve is not empty and does not match the "_SERVICE._PROTO" syntax, then the current record set MUST consist of a single delegation record (Section 8.2.1), a single CNAME record (Section 8.2.3), or one or more GNS2DNS records (Section 8.2.2), which are processed as described in the respective sections below. The record set may include any number of supplemental records. Otherwise, resolution fails and the resolver MUST return an empty record set. Finally, after the recursion terminates, the client preferences for the record type SHOULD be considered. If a VPN record is found and the client requests an A or AAAA record, the VPN record SHOULD be converted (Section 8.2.5) if possible.¶

8.2.1. Encountering zone delegation records

When the resolver encounters a record of a supported zone delegation record type (such as PKEY or EDKEY) and the remainder of the name is not empty, resolution continues recursively with the remainder of the name in the GNS zone specified in the delegation record. Implementations MUST NOT allow multiple different zone type delegations under a single label. Implementations MAY support any subset of zone types. If an unsupported zone type is encountered, resolution fails (NXDOMAIN).¶

If the remainder of the name to resolve is empty and we have received a record set containing only a single PKEY record, the recursion is continued with the PKEY as authoritative zone and the empty apex label "@" as remaining name, except in the case where the desired record type is PKEY, in which case the PKEY record is returned and the resolution is concluded without resolving the empty apex label.¶

8.2.2. GNS2DNS

When a resolver encounters one or more GNS2DNS records and the remaining name is empty and the desired record type is GNS2DNS, the GNS2DNS records are returned.¶

Otherwise, it is expected that the resolver first resolves the IP(s) of the specified DNS name server(s). GNS2DNS records MAY contain numeric IPv4 or IPv6 addresses, allowing the resolver to skip this step. The DNS server names may themselves be names in GNS or DNS. If the DNS server name ends in ".+", the rest of the name is to be interpreted relative to the zone of the GNS2DNS record. If the DNS server name ends in a label representation of a zone key, the DNS server name is to be resolved against the GNS zone zk.¶

Multiple GNS2DNS records may be stored under the same label, in which case the resolver MUST try all of them. The resolver MAY try them in any order or even in parallel. If multiple GNS2DNS records are present, the DNS name MUST be identical for all of them, if not the resolution fails and an emtpy record set is returned as the record set is invalid.¶

Once the IP addresses of the DNS servers have been determined, the DNS name from the GNS2DNS record is appended to the remainder of the name to be resolved, and resolved by querying the DNS name server(s). As the DNS servers specified are possibly authoritative DNS servers, the GNS resolver MUST support recursive resolution and MUST NOT delegate this to the authoritative DNS servers. The first successful recursive name resolution result is returned to the client. In addition, the resolver returns the queried DNS name as a supplemental LEHO record (Section 5.4) with a relative expiration time of one hour.¶

GNS resolvers SHOULD offer a configuration option to disable DNS processing to avoid information leakage and provide a consistent security profile for all name resolutions. Such resolvers would return an empty record set upon encountering a GNS2DNS record during the recursion. However, if GNS2DNS records are encountered in the record set for the apex and a GNS2DNS record is expicitly requested by the application, such records MUST still be returned, even if DNS support is disabled by the GNS resolver configuration.¶

8.2.3. CNAME

If a CNAME record is encountered, the canonical name is appended to the remaining name, except if the remaining name is empty and the desired record type is CNAME, in which case the resolution concludes with the CNAME record. If the canonical name ends in ".+", resolution continues in GNS with the new name in the current zone. Otherwise, the resulting name is resolved via the default operating system name resolution process. This may in turn again trigger a GNS resolution process depending on the system configuration.¶

The recursive DNS resolution process may yield a CNAME as well which in turn may either point into the DNS or GNS namespace (if it ends in a label representation of a zone key). In order to prevent infinite loops, the resolver MUST implement loop detections or limit the number of recursive resolution steps. If the last CNAME was a DNS name, the resolver returns the DNS name as a supplemental LEHO record (Section 5.4) with a relative expiration time of one hour.¶

8.2.4. BOX

When a BOX record is received, a GNS resolver must unbox it if the name to be resolved continues with "_SERVICE._PROTO". Otherwise, the BOX record is to be left untouched. This way, TLSA (and SRV) records do not require a separate network request, and TLSA records become inseparable from the corresponding address records.¶

8.2.5. VPN

At the end of the recursion, if the queried record type is either A or AAAA and the retrieved record set contains at least one VPN record, the resolver SHOULD open a tunnel and return the IPv4 or IPv6 tunnel address, respectively. The type of tunnel depends on the contents of the VPN record data. The VPN record MUST be returned if the resolver implementation does not support setting up a tunnnel.¶

8.2.6. NICK

NICK records are only relevant to the recursive resolver if the record set in question is the final result which is to be returned to the client. The encountered NICK records may either be supplemental (see Section 4) or non-supplemental. If the NICK record is supplemental, the resolver only returns the record set if one of the non-supplemental records matches the queried record type.¶

The differentiation between a supplemental and non-supplemental NICK record allows the client to match the record to the authoritative zone. Consider the following example:¶

Query: alice.example (type=A)
Result:
A: 192.0.2.1
NICK: eve

Figure 14

In this example, the returned NICK record is non-supplemental. For the client, this means that the NICK belongs to the zone "alice.doe" and is published under the empty label along with an A record. The NICK record should be interpreted as: The zone defined by "alice.doe" wants to be referred to as "eve". In contrast, consider the following:¶

Query: alice.example (type=AAAA)
Result:
AAAA: 2001:DB8::1
NICK: john (Supplemental)

Figure 15

In this case, the NICK record is marked as supplemental. This means that the NICK record belongs to the zone "doe" and is published under the label "alice" along with an A record. The NICK record should be interpreted as: The zone defined by "doe" wants to be referred to as "john". This distinction is likely useful for other records published as supplemental.¶

9. Zone Revocation

Whenever a recursive resolver encounters a new GNS zone, it MUST check against the local revocation list whether the respective zone key has been revoked. If the zone key was revoked, the resolution MUST fail with an empty result set.¶

In order to revoke a zone key, a signed revocation object SHOULD be published. This object MUST be signed using the private zone key. The revocation object is flooded in the overlay network. To prevent flooding attacks, the revocation message MUST contain a proof of work (PoW). The revocation message including the PoW MAY be calculated ahead of time to support timely revocation.¶

For all occurences below, "Argon2id" is the Password-based Key Derivation Function as defined in [Argon2]. For the PoW calculations the algorithm is instantiated with the following parameters:¶

S: The salt. Fixed 16-octet string: "GnsRevocationPow".¶
t: Number of iterations: 3¶
m: Memory size in KiB: 1024¶
T: Output length of hash in bytes: 64¶
p: Parallelization parameter: 1¶
v: Algorithm version: 0x13¶
y: Algorithm type (Argon2id): 2¶
X: Unused¶
K: Unused¶

The following is the message string "P" on which the PoW is calculated:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                      POW                      |
+-----------------------------------------------+
|                   TIMESTAMP                   |
+-----------------------------------------------+
|       ZONE TYPE       |    PUBLIC ZONE KEY    |
+-----+-----+-----+-----+                       |
/                                               /
/                                               /
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 16

where:¶

POW: A 64-bit solution to the PoW. In network byte order.¶
TIMESTAMP: denotes the absolute 64-bit date when the revocation was computed. In microseconds since midnight (0 hour), January 1, 1970 in network byte order.¶
PUBLIC KEY: is the 256-bit public key "zk" of the zone which is being revoked and the key to be used to verify SIGNATURE. The wire format of this value is defined in [RFC8032], Section 5.1.5.¶

Traditionally, PoW schemes require to find a "POW" such that at least D leading zeroes are found in the hash result. D is then referred to as the "difficulty" of the PoW. In order to reduce the variance in time it takes to calculate the PoW, we require that a number "Z" different PoWs must be found that on average have "D" leading zeroes.¶

The resulting proofs may then published and disseminated. The concrete dissemination and publication methods are out of scope of this document. Given an average difficulty of "D", the proofs have an expiration time of EPOCH. With each additional bit difficulty, the lifetime of the proof is prolonged for another EPOCH. Consequently, by calculating a more difficult PoW, the lifetime of the proof can be increased on demand by the zone owner.¶

The parameters are defined as follows:¶

Z: The number of PoWs required is fixed at 32.¶
D: The difficulty is fixed at 22.¶
EPOCH: A single epoch is fixed at 365 days.¶

Given that proof has been found, a revocation data object is defined as follows:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   TIMESTAMP                   |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                      TTL                      |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                     POW_0                     |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                       ...                     |
+-----+-----+-----+-----+-----+-----+-----+-----+
|                     POW_Z-1                   |
+-----------------------------------------------+
|       ZONE TYPE       |    PUBLIC ZONE KEY    |
+-----+-----+-----+-----+                       |
/                                               /
/                                               /
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   SIGNATURE                   |
/                                               /
/                                               /
|                                               |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 17

where:¶

TIMESTAMP: denotes the absolute 64-bit date when the revocation was computed. In microseconds since midnight (0 hour), January 1, 1970 in network byte order. This is the same value as the timestamp used in the individual PoW calculations.¶
TTL: denotes the relative 64-bit time to live of of the record in microseconds also in network byte order. This field is informational for a verifier. The verifier may discard revocation if the TTL indicates that it is already expired. However, the actual TTL of the revocation must be determined by examining the leading zeros in the proof of work calculation.¶
POW_i: The values calculated as part of the PoW, in network byte order. Each POW_i MUST be unique in the set of POW values. To facilitate fast verification of uniqueness, the POW values must be given in strictly monotonically increasing order in the message.¶
ZONE TYPE: The 32-bit zone type corresponding to the zone public key.¶
ZONE PUBLIC KEY: is the public key "zk" of the zone which is being revoked and the key to be used to verify SIGNATURE.¶
SIGNATURE: A signature over a timestamp and the public zone zk of the zone which is revoked and corresponds to the key used in the PoW. The signature is created using the Sign() function of the cryptosystem of the zone and the private zone key (see Section 3).¶

The signature over the public key covers a 32-bit pseudo header conceptually prefixed to the public key. The pseudo header includes the key length and signature purpose:¶

0     8     16    24    32    40    48    56
+-----+-----+-----+-----+-----+-----+-----+-----+
|         SIZE (0x30)   |       PURPOSE (0x03)  |
+-----+-----+-----+-----+-----+-----+-----+-----+
|       ZONE TYPE       |     ZONE PUBLIC KEY   |
+-----+-----+-----+-----+                       |
/                                               /
/                                               /
+-----+-----+-----+-----+-----+-----+-----+-----+
|                   TIMESTAMP                   |
+-----+-----+-----+-----+-----+-----+-----+-----+

Figure 18

where:¶

SIZE: A 32-bit value containing the length of the signed data in bytes in network byte order.¶
PURPOSE: A 32-bit signature purpose flag. This field MUST be 3 (in network byte order).¶
ZONE TYPE: The 32-bit zone type corresponding to the zone public key.¶
ZONE PUBLIC KEY / TIMESTAMP: Both values as defined in the revocation data object above.¶

In order to verify a revocation the following steps must be taken, in order:¶

The current time MUST be between TIMESTAMP and TIMESTAMP+TTL.¶
The signature MUST match the public key.¶
The set of POW values MUST NOT contain duplicates.¶
The average number of leading zeroes resulting from the provided POW values D' MUST be greater than D.¶
The validation period (TTL) of the revocation is calculated as (D'-D) * EPOCH * 1.1. The EPOCH is extended by 10% in order to deal with unsynchronized clocks. The TTL added on top of the TIMESTAMP yields the expiration date.¶

11. Security Considerations

11.1. Cryptography

The security of cryptographic systems depends on both the strength of the cryptographic algorithms chosen and the strength of the keys used with those algorithms. The security also depends on the engineering of the protocol used by the system to ensure that there are no non-cryptographic ways to bypass the security of the overall system.¶

This document concerns itself with the selection of cryptographic algorithms for use in GNS. The algorithms identified in this document are not known to be broken (in the cryptographic sense) at the current time, and cryptographic research so far leads us to believe that they are likely to remain secure into the foreseeable future. However, this isn't necessarily forever, and it is expected that new revisions of this document will be issued from time to time to reflect the current best practices in this area.¶

GNS PKEY zone keys use ECDSA over Curve25519. This is an unconventional choice, as ECDSA is usually used with other curves. However, traditional ECDSA curves are problematic for a range of reasons described in the Curve25519 and EdDSA papers. Using EdDSA directly is also not possible, as a hash function is used on the private key which destroys the linearity that the GNU Name System depends upon. We are not aware of anyone suggesting that using Curve25519 instead of another common curve of similar size would lower the security of ECDSA. GNS uses 256-bit curves because that way the encoded (public) keys fit into a single DNS label, which is good for usability.¶

In terms of crypto-agility, whenever the need for an updated cryptographic scheme arises to, for example, replace ECDSA over Curve25519 for PKEY records it may simply be introduced through a new record type. Such a new record type may then replace the delegation record type for future records. The old record type remains and zones can iteratively migrate to the updated zone keys.¶

In order to ensure ciphertext indistinguishability, care must be taken with respect to the initialization vector in the counter block. In our design, the IV is always the expiration time of the record block. For blocks with relative expiration times it is implicitly ensured that each time a block is published into the DHT, its IV is unique as the expiration time is calculated dynamically and increases monotonically. For blocks with absolute expiration times, the implementation MUST ensure that the expiration time is modified when the record data changes. For example. the expiration time may be increased by a single microsecond.¶

11.2. Abuse mitigation

GNS names are UTF-8 strings. Consequently, GNS faces similar issues with respect to name spoofing as DNS does for internationalized domain names. In DNS, attackers may register similar sounding or looking names (see above) in order to execute phishing attacks. GNS zone administrators must take into account this attack vector and incorporate rules in order to mitigate it.¶

Further, DNS can be used to combat illegal content on the internet by having the respective domains seized by authorities. However, the same mechanisms can also be abused in order to impose state censorship, which ist one of the motivations behind GNS. Hence, such a seizure is, by design, difficult to impossible in GNS. In particular, GNS does not support WHOIS ([RFC3912]).¶

11.3. Zone management

In GNS, zone administrators need to manage and protect their zone keys. Once a zone key is lost it cannot be recovered. Once it is compromised it cannot be revoked (unless a revocation message was pre-calculated and is still available). Zone administrators, and for GNS this includes end-users, are required to responsibly and dilligently protect their cryptographic keys. Offline signing is in principle possible, but GNS does not support separate zone signing and key-signing keys (as in [RFC6781]) in order to provide usable security.¶

Similarly, users are required to manage their local root zone. In order to ensure integrity and availability or names, users must ensure that their local root zone information is not compromised or outdated. It can be expected that the processing of zone revocations and an initial root zone is provided with a GNS client implementation ("drop shipping"). Extension and customization of the zone is at the full discretion of the user.¶

11.4. Impact of underlying DHT

This document does not specifiy the properties of the underlying distributed hash table (DHT) which is required by any GNS implementation. For implementors, it is important to note that the properties of the DHT are directly inherited by the GNS implementation. This includes both security as well as other non-functional properties such as scalability and performance. Implementors should take great care when selecting or implementing a DHT for use in a GNS implementation. DHTs with strong security and performance guarantees exist [R5N]. It should also be taken into consideration that GNS implementations which build upon different DHT overlays are unlikely to be interoperable with each other.¶

11.5. Revocations

Zone administrators are advised to pre-generate zone revocations and securely store the revocation information in case the zone key is lost, compromised or replaced in the furture. Pre-calculated revocations may become invalid due to expirations or protocol changes such as epoch adjustments. Consequently, implementors and users must make precautions in order to manage revocations accordingly.¶

Revocation payloads do NOT include a 'new' key for key replacement. Inclusion of such a key would have two major disadvantages:¶

If revocation is used after a private key was compromised, allowing key replacement would be dangerous: if an adversary took over the private key, the adversary could then broadcast a revocation with a key replacement. For the replacement, the compromised owner would have no chance to issue even a revocation. Thus, allowing a revocation message to replace a private key makes dealing with key compromise situations worse.¶

Sometimes, key revocations are used with the objective of changing cryptosystems. Migration to another cryptosystem by replacing keys via a revocation message would only be secure as long as both cryptosystems are still secure against forgery. Such a planned, non-emergency migration to another cryptosystem should be done by running zones for both ciphersystems in parallel for a while. The migration would conclude by revoking the legacy zone key only once it is deemed no longer secure, and hopefully after most users have migrated to the replacement.¶

14. Normative References

[RFC1034]: Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, <https://www.rfc-editor.org/info/rfc1034>.
[RFC1035]: Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC2782]: Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, DOI 10.17487/RFC2782, February 2000, <https://www.rfc-editor.org/info/rfc2782>.
[RFC2119]: Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC3629]: Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2003, <https://www.rfc-editor.org/info/rfc3629>.
[RFC3686]: Housley, R., "Using Advanced Encryption Standard (AES) Counter Mode With IPsec Encapsulating Security Payload (ESP)", RFC 3686, DOI 10.17487/RFC3686, January 2004, <https://www.rfc-editor.org/info/rfc3686>.
[RFC3826]: Blumenthal, U., Maino, F., and K. McCloghrie, "The Advanced Encryption Standard (AES) Cipher Algorithm in the SNMP User-based Security Model", RFC 3826, DOI 10.17487/RFC3826, June 2004, <https://www.rfc-editor.org/info/rfc3826>.
[RFC3912]: Daigle, L., "WHOIS Protocol Specification", RFC 3912, DOI 10.17487/RFC3912, September 2004, <https://www.rfc-editor.org/info/rfc3912>.
[RFC4648]: Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, <https://www.rfc-editor.org/info/rfc4648>.
[RFC5869]: Krawczyk, H. and P. Eronen, "HMAC-based Extract-and-Expand Key Derivation Function (HKDF)", RFC 5869, DOI 10.17487/RFC5869, May 2010, <https://www.rfc-editor.org/info/rfc5869>.
[RFC5890]: Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, <https://www.rfc-editor.org/info/rfc5890>.
[RFC5891]: Klensin, J., "Internationalized Domain Names in Applications (IDNA): Protocol", RFC 5891, DOI 10.17487/RFC5891, August 2010, <https://www.rfc-editor.org/info/rfc5891>.
[RFC6781]: Kolkman, O., Mekking, W., and R. Gieben, "DNSSEC Operational Practices, Version 2", RFC 6781, DOI 10.17487/RFC6781, December 2012, <https://www.rfc-editor.org/info/rfc6781>.
[RFC6895]: Eastlake 3rd, D., "Domain Name System (DNS) IANA Considerations", BCP 42, RFC 6895, DOI 10.17487/RFC6895, April 2013, <https://www.rfc-editor.org/info/rfc6895>.
[RFC6979]: Pornin, T., "Deterministic Usage of the Digital Signature Algorithm (DSA) and Elliptic Curve Digital Signature Algorithm (ECDSA)", RFC 6979, DOI 10.17487/RFC6979, August 2013, <https://www.rfc-editor.org/info/rfc6979>.
[RFC7748]: Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves for Security", RFC 7748, DOI 10.17487/RFC7748, January 2016, <https://www.rfc-editor.org/info/rfc7748>.
[RFC8032]: Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital Signature Algorithm (EdDSA)", RFC 8032, DOI 10.17487/RFC8032, January 2017, <https://www.rfc-editor.org/info/rfc8032>.
[RFC8126]: Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.
[GANA]: GNUnet e.V., "GNUnet Assigned Numbers Authority (GANA)", April 2020, <https://gana.gnunet.org/>.
[GNS]: Wachs, M., Schanzenbach, M., and C. Grothoff, "A Censorship-Resistant, Privacy-Enhancing and Fully Decentralized Name System", 2014, <https://doi.org/10.1007/978-3-319-12280-9_9>.
[R5N]: Evans, N. S. and C. Grothoff, "R5N: Randomized recursive routing for restricted-route networks", 2011, <https://doi.org/10.1109/ICNSS.2011.6060022>.
[Argon2]: Biryukov, A., Dinu, D., Khovratovich, D., and S. Josefsson, "The memory-hard Argon2 password hash and proof-of-work function", March 2020, <https://datatracker.ietf.org/doc/draft-irtf-cfrg-argon2/>.
[MODES]: Dworkin, M., "Recommendation for Block Cipher Modes of Operation: Methods and Techniques", December 2001, <https://doi.org/10.6028/NIST.SP.800-38A>.
[GCM]: Dworkin, M., "Recommendation for Block Cipher Modes of Operation: Galois/Counter Mode (GCM) and GMAC", November 2007, <https://doi.org/10.6028/NIST.SP.800-38D>.
[CrockfordB32]: Douglas, D., "Base32", March 2019, <https://www.crockford.com/base32.html>.
[Tor224]: Goulet, D., Kadianakis, G., and N. Mathewson, "Next-Generation Hidden Services in Tor", November 2013, <https://gitweb.torproject.org/torspec.git/tree/proposals/224-rend-spec-ng.txt#n2135>.
[ed25519]: Bernstein, D., Duif, N., Lange, T., Schwabe, P., and B. Yang, "High-Speed High-Security Signatures", 2011, <http://link.springer.com/chapter/10.1007/978-3-642-23951-9_9>.