feat: Add support for converting KeyPairs into JWKs

Signed-off-by: Joonas Bergius <[email protected]>

Cargo.toml

@@ -24,6 +24,8 @@ cli = [
 
 xkeys = ["dep:crypto_box"]
 
+jwk = ["serde", "serde_json", "sha2"]
+
 [[bin]]
 name = "nk"
 required-features = ["cli"]
@@ -47,6 +49,10 @@ exitfailure = { version = "0.5.1", optional = true }
 env_logger = { version = "0.9", optional = true }
 serde_json = { version = "1.0", optional = true }
 
+# jwk dependencies
+serde = { version = "1.0", optional = true, features = ["derive"] }
+sha2 = { version = "0.10", optional = true }
+
 [target.'cfg(target_arch = "wasm32")'.dependencies]
 # NOTE: We need this due to an underlying dependency being pulled in by
 # `ed25519-dalek`. Even if we exclude `rand`, that crate pulls it in. `rand` pulls in the low level

src/error.rs

@@ -42,6 +42,8 @@ pub enum ErrorKind {
     IncorrectKeyType,
     /// Payload not valid (or failed to be decrypted)
     InvalidPayload,
+    /// Thumbprint could not be calculated over the provided public key value
+    ThumbprintCalculationFailure,
 }
 
 /// A handy macro borrowed from the `signatory` crate that lets library-internal code generate
@@ -70,6 +72,7 @@ impl ErrorKind {
             ErrorKind::SignatureError => "Signature failure",
             ErrorKind::IncorrectKeyType => "Incorrect key type",
             ErrorKind::InvalidPayload => "Invalid payload",
+            ErrorKind::ThumbprintCalculationFailure => "Thumbprint calculation failure",
         }
     }
 }

src/jwk.rs

@@ -0,0 +1,151 @@
+use std::collections::BTreeMap;
+
+use crate::{err, from_public_key, from_seed, KeyPair, KeyPairType, Result};
+use data_encoding::BASE64URL_NOPAD;
+use ed25519_dalek::{SigningKey, VerifyingKey};
+use serde::{Deserialize, Serialize};
+use serde_json::json;
+use sha2::{Digest, Sha256};
+
+// We hard code the value here, because we're using Edwards-curve keys, which OKP represents:
+// https://datatracker.ietf.org/doc/html/draft-ietf-jose-cfrg-curves-06#section-2
+const JWK_KEY_TYPE: &str = "OKP";
+// https://datatracker.ietf.org/doc/html/draft-ietf-jose-cfrg-curves-06#section-3.1
+const JWK_ALGORITHM: &str = "EdDSA";
+const JWK_SUBTYPE: &str = "Ed25519";
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct JsonWebKey {
+    /// Intended use of the JWK, this is based on the KeyPairType of the KeyPair the JWK is based on, using "enc" for KeyPairType::Curve, otherwise "sig"
+    #[serde(rename = "use")]
+    intended_use: String,
+    /// Key type, which we default to OKP (Octet Key Pair) to represent Edwards-curve keys
+    #[serde(rename = "kty")]
+    key_type: String,
+    /// Key ID, which will be represented by the thumbprint calculated over the subtype (crv), key_type (kty) and public_key (x) components of the JWK.
+    /// See https://datatracker.ietf.org/doc/html/rfc7639 for more details.
+    #[serde(rename = "kid")]
+    key_id: String,
+    /// Algorithm used for the JWK, defaults to EdDSA
+    #[serde(rename = "alg")]
+    algorithm: String,
+    /// Subtype of the key (from the "JSON Web Elliptic Curve" registry)
+    #[serde(rename = "crv")]
+    subtype: String,
+    // Public key value encoded using base64url encoding
+    #[serde(rename = "x")]
+    public_key: String,
+    // Private key value, if provided, encoded using base64url encoding
+    #[serde(rename = "d", skip_serializing_if = "Option::is_none")]
+    private_key: Option<String>,
+}
+
+impl JsonWebKey {
+    pub fn from_seed(source: &str) -> Result<Self> {
+        let (prefix, seed) = from_seed(source)?;
+        let sk = SigningKey::from_bytes(&seed);
+        let kp_type = &KeyPairType::from(prefix);
+        let public_key = BASE64URL_NOPAD.encode(sk.verifying_key().as_bytes());
+        let thumbprint = Self::calculate_thumbprint(&public_key)?;
+
+        Ok(JsonWebKey {
+            intended_use: Self::intended_use_for_key_pair_type(kp_type),
+            key_id: thumbprint,
+            public_key,
+            private_key: Some(BASE64URL_NOPAD.encode(sk.as_bytes())),
+            ..Default::default()
+        })
+    }
+
+    pub fn from_public_key(source: &str) -> Result<Self> {
+        let (prefix, bytes) = from_public_key(source)?;
+        let vk = VerifyingKey::from_bytes(&bytes)?;
+        let public_key = BASE64URL_NOPAD.encode(vk.as_bytes());
+        let thumbprint = Self::calculate_thumbprint(&public_key)?;
+
+        Ok(JsonWebKey {
+            intended_use: Self::intended_use_for_key_pair_type(&KeyPairType::from(prefix)),
+            key_id: thumbprint,
+            public_key,
+            ..Default::default()
+        })
+    }
+
+    fn intended_use_for_key_pair_type(typ: &KeyPairType) -> String {
+        match typ {
+            KeyPairType::Server
+            | KeyPairType::Cluster
+            | KeyPairType::Operator
+            | KeyPairType::Account
+            | KeyPairType::User
+            | KeyPairType::Module
+            | KeyPairType::Service => "sig".to_owned(),
+            KeyPairType::Curve => "enc".to_owned(),
+        }
+    }
+
+    /// For details on how fingerprints are calculated, see: https://datatracker.ietf.org/doc/html/rfc7638#section-3.1
+    /// For OKP specific details, see https://datatracker.ietf.org/doc/html/draft-ietf-jose-cfrg-curves-06#appendix-A.3
+    pub fn calculate_thumbprint(public_key: &str) -> Result<String> {
+        // We use BTreeMap here, because the order needs to be lexicographically sorted:
+        // https://datatracker.ietf.org/doc/html/rfc7638#section-3.3
+        let components = BTreeMap::from([
+            ("crv", JWK_SUBTYPE),
+            ("kty", JWK_KEY_TYPE),
+            ("x", public_key),
+        ]);
+        let value = json!(components);
+        let mut bytes: Vec<u8> = Vec::new();
+        serde_json::to_writer(&mut bytes, &value).map_err(|_| {
+            err!(
+                ThumbprintCalculationFailure,
+                "unable to serialize public key"
+            )
+        })?;
+        let mut hasher = Sha256::new();
+        hasher.update(&*bytes);
+        let hash = hasher.finalize();
+        Ok(BASE64URL_NOPAD.encode(&hash))
+    }
+}
+
+impl Default for JsonWebKey {
+    fn default() -> Self {
+        Self {
+            intended_use: Default::default(),
+            key_type: JWK_KEY_TYPE.to_string(),
+            key_id: Default::default(),
+            algorithm: JWK_ALGORITHM.to_string(),
+            subtype: JWK_SUBTYPE.to_string(),
+            public_key: Default::default(),
+            private_key: None,
+        }
+    }
+}
+
+impl TryFrom<KeyPair> for JsonWebKey {
+    type Error = crate::error::Error;
+
+    fn try_from(value: KeyPair) -> Result<Self> {
+        if let Ok(seed) = value.seed() {
+            Ok(Self::from_seed(&seed)?)
+        } else {
+            Ok(Self::from_public_key(&value.public_key())?)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Using the example values from https://datatracker.ietf.org/doc/html/draft-ietf-jose-cfrg-curves-06#appendix-A.3
+    #[test]
+    fn calculate_thumbprint_provides_correct_thumbprint() {
+        let input_public_key = "11qYAYKxCrfVS_7TyWQHOg7hcvPapiMlrwIaaPcHURo";
+        let expected_thumbprint = "kPrK_qmxVWaYVA9wwBF6Iuo3vVzz7TxHCTwXBygrS4k";
+        let actual_thumbprint = JsonWebKey::calculate_thumbprint(input_public_key).unwrap();
+
+        assert_eq!(expected_thumbprint, actual_thumbprint);
+    }
+}

src/lib.rs

@@ -58,6 +58,12 @@ mod xkeys;
 #[cfg(feature = "xkeys")]
 pub use xkeys::XKey;
 
+#[cfg(feature = "jwk")]
+mod jwk;
+
+#[cfg(feature = "jwk")]
+pub use jwk::JsonWebKey;
+
 const ENCODED_SEED_LENGTH: usize = 58;
 const ENCODED_PUBKEY_LENGTH: usize = 56;
 
@@ -287,33 +293,17 @@ impl KeyPair {
 
     /// Attempts to produce a public-only key pair from the given encoded public key string
     pub fn from_public_key(source: &str) -> Result<KeyPair> {
-        if source.len() != ENCODED_PUBKEY_LENGTH {
-            let l = source.len();
-            return Err(err!(InvalidKeyLength, "Bad key length: {}", l));
-        }
+        let (prefix, bytes) = from_public_key(source)?;
 
-        let source_bytes = source.as_bytes();
-        let mut raw = decode_raw(source_bytes)?;
+        let pk = VerifyingKey::from_bytes(&bytes)
+            .map_err(|_| err!(VerifyError, "Could not read public key"))?;
 
-        let prefix = raw[0];
-        if !valid_public_key_prefix(prefix) {
-            Err(err!(
-                InvalidPrefix,
-                "Not a valid public key prefix: {}",
-                raw[0]
-            ))
-        } else {
-            raw.remove(0);
-            match VerifyingKey::try_from(&raw[..]) {
-                Ok(pk) => Ok(KeyPair {
-                    kp_type: KeyPairType::from(prefix),
-                    pk,
-                    sk: None,
-                    signing_key: None,
-                }),
-                Err(_) => Err(err!(VerifyError, "Could not read public key")),
-            }
-        }
+        Ok(KeyPair {
+            kp_type: KeyPairType::from(prefix),
+            pk,
+            sk: None,
+            signing_key: None,
+        })
     }
 
     /// Attempts to produce a full key pair from the given encoded seed string
@@ -348,6 +338,32 @@ fn decode_raw(raw: &[u8]) -> Result<Vec<u8>> {
     }
 }
 
+/// Returns the prefix byte and the underlying public key bytes
+fn from_public_key(source: &str) -> Result<(u8, [u8; 32])> {
+    if source.len() != ENCODED_PUBKEY_LENGTH {
+        let l = source.len();
+        return Err(err!(InvalidKeyLength, "Bad key length: {}", l));
+    }
+
+    let source_bytes = source.as_bytes();
+    let mut raw = decode_raw(source_bytes)?;
+
+    let prefix = raw[0];
+    if !valid_public_key_prefix(prefix) {
+        return Err(err!(
+            InvalidPrefix,
+            "Not a valid public key prefix: {}",
+            raw[0]
+        ));
+    }
+    raw.remove(0);
+
+    let mut public_key = [0u8; 32];
+    public_key.copy_from_slice(&raw[..]);
+
+    Ok((prefix, public_key))
+}
+
 /// Returns the type and the seed
 fn from_seed(source: &str) -> Result<(u8, [u8; 32])> {
     if source.len() != ENCODED_SEED_LENGTH {
@@ -521,6 +537,16 @@ mod tests {
         }
     }
 
+    #[test]
+    fn from_public_key_rejects_bad_prefix() {
+        let public_key = "ZCO4XYNKEN7ZFQ42BHYCBYI3K7USOGG43C2DIJZYWSQ2YEMBOZWN6PYH";
+        let pair = KeyPair::from_public_key(public_key);
+        assert!(pair.is_err());
+        if let Err(e) = pair {
+            assert_eq!(e.kind(), ErrorKind::InvalidPrefix);
+        }
+    }
+
     #[test]
     fn public_key_round_trip() {
         let account =