ssi-sd-jwt implementation

Cargo.toml

@@ -65,6 +65,7 @@ ssi-ucan = { path = "./ssi-ucan", version = "0.1" }
 ssi-vc = { path = "./ssi-vc", version = "0.2.0" }
 ssi-zcap-ld = { path = "./ssi-zcap-ld", version = "0.1.2" }
 ssi-caips = { path = "./ssi-caips", version = "0.1", default-features = false }
+ssi-sd-jwt = { path = "./ssi-sd-jwt", version = "0.1" }
 
 [workspace]
 members = [
@@ -88,6 +89,7 @@ members = [
   "ssi-dids",
   "ssi-jws",
   "ssi-jwt",
+  "ssi-sd-jwt",
   "ssi-tzkey",
   "ssi-ssh",
   "ssi-ldp",

src/lib.rs

@@ -64,6 +64,7 @@ pub use ssi_ldp as ldp;
 pub use ssi_ldp::eip712;
 #[deprecated = "Use ssi::ldp::soltx"]
 pub use ssi_ldp::soltx;
+pub use ssi_sd_jwt as sd_jwt;
 pub use ssi_ssh as ssh;
 pub use ssi_tzkey as tzkey;
 pub use ssi_ucan as ucan;

ssi-sd-jwt/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "ssi-sd-jwt"
+version = "0.1.0"
+edition = "2021"
+authors = ["Spruce Systems, Inc."]
+license = "Apache-2.0"
+description = "Implementation of SD-JWT for the ssi library."
+repository = "https://github.com/spruceid/ssi/"
+documentation = "https://docs.rs/ssi-sd-jwt/"
+
+[dependencies]
+base64 = "0.12"
+rand = { version = "0.8" }
+serde = { version = "1.0", features = ["derive"] }
+serde_json = "1.0"
+sha2 = "0.10"
+ssi-jwk = { path = "../ssi-jwk", version = "0.1" }
+ssi-jws = { path = "../ssi-jws", version = "0.1" }
+ssi-jwt = { path = "../ssi-jwt", version = "0.1" }
+thiserror = "1.0"
+
+[dev-dependencies]
+hex-literal = "0.4.1"

ssi-sd-jwt/src/decode.rs

@@ -0,0 +1,213 @@
+use serde::de::DeserializeOwned;
+use ssi_jwk::JWK;
+use std::collections::BTreeMap;
+
+use crate::disclosure::{DecodedDisclosure, DisclosureKind};
+use crate::serialized::deserialize_string_format;
+use crate::*;
+
+/// High level API to decode a fully encoded SD-JWT.  That is a JWT and selective
+/// disclosures separated by tildes
+pub fn decode_verify<Claims: DeserializeOwned>(
+    serialized: &str,
+    key: &JWK,
+) -> Result<Claims, DecodeError> {
+    let deserialized = deserialize_string_format(serialized)
+        .ok_or(DecodeError::UnableToDeserializeStringFormat)?;
+
+    decode_verify_disclosure_array(deserialized, key)
+}
+
+/// Lower level API to decode an SD-JWT that has already been split into its
+/// JWT and disclosure components
+pub fn decode_verify_disclosure_array<Claims: DeserializeOwned>(
+    deserialized: Deserialized<'_>,
+    key: &JWK,
+) -> Result<Claims, DecodeError> {
+    let mut payload_claims: serde_json::Value = ssi_jwt::decode_verify(deserialized.jwt, key)?;
+
+    let sd_alg = extract_sd_alg(&mut payload_claims)?;
+
+    let mut disclosures = translate_to_in_progress_disclosures(&deserialized.disclosures, sd_alg)?;
+
+    visit_claims(&mut payload_claims, &mut disclosures)?;
+
+    for (_, disclosure) in disclosures {
+        if !disclosure.found {
+            return Err(DecodeError::UnusedDisclosure);
+        }
+    }
+
+    Ok(serde_json::from_value(payload_claims)?)
+}
+
+fn extract_sd_alg(claims: &mut serde_json::Value) -> Result<SdAlg, DecodeError> {
+    let claims = claims.as_object_mut().ok_or(DecodeError::ClaimsWrongType)?;
+
+    let sd_alg_claim = claims
+        .remove(SD_ALG_CLAIM_NAME)
+        .ok_or(DecodeError::MissingSdAlg)?;
+
+    let sd_alg = sd_alg_claim.as_str().ok_or(DecodeError::SdAlgWrongType)?;
+
+    SdAlg::try_from(sd_alg)
+}
+
+fn translate_to_in_progress_disclosures(
+    disclosures: &[&str],
+    sd_alg: SdAlg,
+) -> Result<BTreeMap<String, InProgressDisclosure>, DecodeError> {
+    let disclosure_vec: Result<Vec<_>, DecodeError> = disclosures
+        .iter()
+        .map(|disclosure| InProgressDisclosure::new(disclosure, sd_alg))
+        .collect();
+
+    let disclosure_vec = disclosure_vec?;
+
+    let mut disclosure_map = BTreeMap::new();
+    for disclosure in disclosure_vec {
+        let prev = disclosure_map.insert(disclosure.hash.clone(), disclosure);
+
+        if prev.is_some() {
+            return Err(DecodeError::MultipleDisclosuresWithSameHash);
+        }
+    }
+
+    Ok(disclosure_map)
+}
+
+#[derive(Debug)]
+struct InProgressDisclosure {
+    decoded: DecodedDisclosure,
+    hash: String,
+    found: bool,
+}
+
+impl InProgressDisclosure {
+    fn new(disclosure: &str, sd_alg: SdAlg) -> Result<Self, DecodeError> {
+        Ok(InProgressDisclosure {
+            decoded: DecodedDisclosure::new(disclosure)?,
+            hash: hash_encoded_disclosure(sd_alg, disclosure),
+            found: false,
+        })
+    }
+}
+
+fn visit_claims(
+    payload_claims: &mut serde_json::Value,
+    disclosures: &mut BTreeMap<String, InProgressDisclosure>,
+) -> Result<(), DecodeError> {
+    let payload_claims = match payload_claims.as_object_mut() {
+        Some(obj) => obj,
+        None => return Ok(()),
+    };
+
+    // Visit children
+    for (_, child_claim) in payload_claims.iter_mut() {
+        visit_claims(child_claim, disclosures)?
+    }
+
+    // Process _sd claim
+    let new_claims = if let Some(sd_claims) = payload_claims.remove(SD_CLAIM_NAME) {
+        decode_sd_claims(&sd_claims, disclosures)?
+    } else {
+        vec![]
+    };
+
+    for (new_claim_name, mut new_claim_value) in new_claims {
+        visit_claims(&mut new_claim_value, disclosures)?;
+
+        let prev = payload_claims.insert(new_claim_name, new_claim_value);
+
+        if prev.is_some() {
+            return Err(DecodeError::DisclosureClaimCollidesWithJwtClaim);
+        }
+    }
+
+    // Process array claims
+    for (_, item) in payload_claims.iter_mut() {
+        if let Some(array) = item.as_array_mut() {
+            let mut new_array_items = decode_array_claims(array, disclosures)?;
+
+            for item in new_array_items.iter_mut() {
+                visit_claims(item, disclosures)?;
+            }
+
+            *array = new_array_items;
+        }
+    }
+
+    Ok(())
+}
+
+fn decode_sd_claims(
+    sd_claims: &serde_json::Value,
+    disclosures: &mut BTreeMap<String, InProgressDisclosure>,
+) -> Result<Vec<(String, serde_json::Value)>, DecodeError> {
+    let sd_claims = sd_claims
+        .as_array()
+        .ok_or(DecodeError::SdPropertyNotArray)?;
+    let mut found_disclosures = vec![];
+    for disclosure_hash in sd_claims {
+        let disclosure_hash = disclosure_hash
+            .as_str()
+            .ok_or(DecodeError::SdClaimNotString)?;
+
+        if let Some(in_progress_disclosure) = disclosures.get_mut(disclosure_hash) {
+            if in_progress_disclosure.found {
+                return Err(DecodeError::DisclosureUsedMultipleTimes);
+            }
+            in_progress_disclosure.found = true;
+            match in_progress_disclosure.decoded.kind {
+                DisclosureKind::ArrayItem(_) => {
+                    return Err(DecodeError::ArrayDisclosureWhenExpectingProperty)
+                }
+                DisclosureKind::Property {
+                    ref name,
+                    ref value,
+                } => found_disclosures.push((name.clone(), value.clone())),
+            }
+        }
+    }
+
+    Ok(found_disclosures)
+}
+
+fn decode_array_claims(
+    array: &[serde_json::Value],
+    disclosures: &mut BTreeMap<String, InProgressDisclosure>,
+) -> Result<Vec<serde_json::Value>, DecodeError> {
+    let mut new_items = vec![];
+    for item in array.iter() {
+        if let Some(hash) = array_item_is_disclosure(item) {
+            if let Some(in_progress_disclosure) = disclosures.get_mut(hash) {
+                if in_progress_disclosure.found {
+                    return Err(DecodeError::DisclosureUsedMultipleTimes);
+                }
+                in_progress_disclosure.found = true;
+                match in_progress_disclosure.decoded.kind {
+                    DisclosureKind::ArrayItem(ref value) => {
+                        new_items.push(value.clone());
+                    }
+                    DisclosureKind::Property { .. } => {
+                        return Err(DecodeError::PropertyDisclosureWhenExpectingArray)
+                    }
+                }
+            }
+        } else {
+            new_items.push(item.clone());
+        }
+    }
+
+    Ok(new_items)
+}
+
+fn array_item_is_disclosure(item: &serde_json::Value) -> Option<&str> {
+    let obj = item.as_object()?;
+
+    if obj.len() != 1 {
+        return None;
+    }
+
+    obj.get(ARRAY_CLAIM_ITEM_PROPERTY_NAME)?.as_str()
+}

ssi-sd-jwt/src/digest.rs

@@ -0,0 +1,69 @@
+use base64::URL_SAFE_NO_PAD;
+use sha2::Digest;
+
+use crate::DecodeError;
+
+/// Elements of the _sd_alg claim
+#[non_exhaustive]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum SdAlg {
+    /// SHA-256 Algortim for hashing disclosures
+    Sha256,
+}
+
+impl SdAlg {
+    const SHA256_STR: &'static str = "sha-256";
+}
+
+impl SdAlg {
+    /// String encoding of _sd_alg field
+    pub fn to_str(&self) -> &'static str {
+        match self {
+            SdAlg::Sha256 => Self::SHA256_STR,
+        }
+    }
+}
+
+impl TryFrom<&str> for SdAlg {
+    type Error = DecodeError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        Ok(match value {
+            Self::SHA256_STR => SdAlg::Sha256,
+            other => return Err(DecodeError::UnknownSdAlg(other.to_owned())),
+        })
+    }
+}
+
+impl From<SdAlg> for &'static str {
+    fn from(value: SdAlg) -> Self {
+        value.to_str()
+    }
+}
+
+/// Lower level API to generate the hash of a given disclosure string already converted
+/// into base 64
+pub fn hash_encoded_disclosure(digest_algo: SdAlg, disclosure: &str) -> String {
+    match digest_algo {
+        SdAlg::Sha256 => {
+            let digest = sha2::Sha256::digest(disclosure.as_bytes());
+            base64::encode_config(digest, URL_SAFE_NO_PAD)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_disclosure_hashing() {
+        assert_eq!(
+            hash_encoded_disclosure(
+                SdAlg::Sha256,
+                "WyI2cU1RdlJMNWhhaiIsICJmYW1pbHlfbmFtZSIsICJNw7ZiaXVzIl0"
+            ),
+            "uutlBuYeMDyjLLTpf6Jxi7yNkEF35jdyWMn9U7b_RYY",
+        );
+    }
+}