auths_crypto/
did_key.rs

1//! DID:key encoding and decoding for Ed25519 public keys.
2//!
3//! Centralizes all `did:key` ↔ Ed25519 byte conversions in one place.
4//! The `did:key` method encodes a public key directly in the DID string
5//! using multicodec + base58btc, per the [did:key spec](https://w3c-ccg.github.io/did-method-key/).
6
7/// Ed25519 multicodec prefix (varint-encoded `0xED`).
8const ED25519_MULTICODEC: [u8; 2] = [0xED, 0x01];
9
10/// Errors from parsing or encoding `did:key` strings.
11#[derive(Debug, Clone, thiserror::Error, PartialEq, Eq)]
12pub enum DidKeyError {
13    #[error("DID must start with 'did:key:z', got: {0}")]
14    InvalidPrefix(String),
15
16    #[error("Base58 decoding failed: {0}")]
17    Base58DecodeFailed(String),
18
19    #[error("Unsupported or malformed multicodec: expected Ed25519 [0xED, 0x01]")]
20    UnsupportedMulticodec,
21
22    #[error("Invalid Ed25519 key length: expected 32 bytes, got {0}")]
23    InvalidKeyLength(usize),
24}
25
26/// Decode a `did:key:z...` string into a 32-byte Ed25519 public key.
27///
28/// Args:
29/// * `did`: A DID string in `did:key:z<base58btc>` format.
30///
31/// Usage:
32/// ```ignore
33/// let pk: [u8; 32] = did_key_to_ed25519("did:key:z6Mkf...")?;
34/// ```
35pub fn did_key_to_ed25519(did: &str) -> Result<[u8; 32], DidKeyError> {
36    let encoded = strip_did_key_prefix(did)?;
37    let decoded = decode_base58(encoded)?;
38    validate_multicodec_and_extract(&decoded)
39}
40
41/// Encode a 32-byte Ed25519 public key as a `did:key:z...` string.
42///
43/// Args:
44/// * `public_key`: A 32-byte Ed25519 public key.
45///
46/// Usage:
47/// ```ignore
48/// let did = ed25519_pubkey_to_did_key(&key_bytes);
49/// assert!(did.starts_with("did:key:z"));
50/// ```
51pub fn ed25519_pubkey_to_did_key(public_key: &[u8; 32]) -> String {
52    let mut prefixed = vec![0xED, 0x01];
53    prefixed.extend_from_slice(public_key);
54    let encoded = bs58::encode(prefixed).into_string();
55    format!("did:key:z{encoded}")
56}
57
58/// Encode a raw public key as a `did:keri:` string (base58-encoded).
59///
60/// Args:
61/// * `pk`: Raw public key bytes.
62pub fn ed25519_pubkey_to_did_keri(pk: &[u8]) -> String {
63    format!("did:keri:{}", bs58::encode(pk).into_string())
64}
65
66fn strip_did_key_prefix(did: &str) -> Result<&str, DidKeyError> {
67    did.strip_prefix("did:key:z")
68        .ok_or_else(|| DidKeyError::InvalidPrefix(did.to_string()))
69}
70
71fn decode_base58(encoded: &str) -> Result<Vec<u8>, DidKeyError> {
72    bs58::decode(encoded)
73        .into_vec()
74        .map_err(|e| DidKeyError::Base58DecodeFailed(e.to_string()))
75}
76
77fn validate_multicodec_and_extract(decoded: &[u8]) -> Result<[u8; 32], DidKeyError> {
78    if decoded.len() != 34
79        || decoded[0] != ED25519_MULTICODEC[0]
80        || decoded[1] != ED25519_MULTICODEC[1]
81    {
82        if decoded.len() != 34 {
83            return Err(DidKeyError::InvalidKeyLength(
84                decoded.len().saturating_sub(2),
85            ));
86        }
87        return Err(DidKeyError::UnsupportedMulticodec);
88    }
89
90    let mut key = [0u8; 32];
91    key.copy_from_slice(&decoded[2..]);
92    Ok(key)
93}
94
95#[cfg(test)]
96mod tests {
97    use super::*;
98
99    #[test]
100    fn roundtrip_encode_decode() {
101        let original = [42u8; 32];
102        let did = ed25519_pubkey_to_did_key(&original);
103        assert!(did.starts_with("did:key:z"));
104        let decoded = did_key_to_ed25519(&did).unwrap();
105        assert_eq!(decoded, original);
106    }
107
108    #[test]
109    fn rejects_invalid_prefix() {
110        let err = did_key_to_ed25519("did:web:example.com").unwrap_err();
111        assert!(matches!(err, DidKeyError::InvalidPrefix(_)));
112    }
113
114    #[test]
115    fn rejects_invalid_base58() {
116        let err = did_key_to_ed25519("did:key:z0OOO").unwrap_err();
117        assert!(matches!(err, DidKeyError::Base58DecodeFailed(_)));
118    }
119}
auths_crypto/did_key.rs

auths_crypto/
did_key.rs
