Add canonicalize_object function

src/json_signatures/canonicalization.rs

@@ -0,0 +1,13 @@
+use serde::Serialize;
+
+#[derive(thiserror::Error, Debug)]
+#[error("canonicalization error")]
+pub struct CanonicalizationError(#[from] serde_json::Error);
+
+/// JCS: https://www.rfc-editor.org/rfc/rfc8785
+pub fn canonicalize_object(
+    object: &impl Serialize,
+) -> Result<String, CanonicalizationError> {
+    let object_str = serde_jcs::to_string(object)?;
+    Ok(object_str)
+}

src/json_signatures/create.rs

@@ -4,6 +4,7 @@ use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
 use crate::utils::crypto::sign_message;
+use super::canonicalization::{canonicalize_object, CanonicalizationError};
 
 /// Data Integrity Proof
 /// https://w3c.github.io/vc-data-integrity/
@@ -31,6 +32,9 @@ pub enum JsonSignatureError {
     #[error(transparent)]
     JsonError(#[from] serde_json::Error),
 
+    #[error(transparent)]
+    CanonicalizationError(#[from] CanonicalizationError),
+
     #[error("signing error")]
     SigningError(#[from] rsa::errors::Error),
 
@@ -44,10 +48,9 @@ pub fn sign_object(
     signer_key_id: &str,
 ) -> Result<Value, JsonSignatureError> {
     // Canonicalize
-    // JCS: https://www.rfc-editor.org/rfc/rfc8785
+    let message = canonicalize_object(object)?;
-    let object_str = serde_jcs::to_string(object)?;
     // Sign
-    let signature_b64 = sign_message(signer_key, &object_str)?;
+    let signature_b64 = sign_message(signer_key, &message)?;
     // Insert proof
     let proof = Proof {
         proof_type: PROOF_TYPE.to_string(),

src/json_signatures/mod.rs

@@ -1,2 +1,3 @@
+mod canonicalization;
 pub mod create;
 pub mod verify;

src/json_signatures/verify.rs

@@ -2,6 +2,7 @@ use rsa::RsaPublicKey;
 use serde_json::Value;
 
 use crate::utils::crypto::verify_signature;
+use super::canonicalization::{canonicalize_object, CanonicalizationError};
 use super::create::{Proof, PROOF_TYPE, PROOF_PURPOSE};
 
 pub struct SignatureData {
@@ -21,8 +22,8 @@ pub enum JsonSignatureVerificationError {
     #[error("{0}")]
     InvalidProof(&'static str),
 
-    #[error("canonicalization error")]
+    #[error(transparent)]
-    CanonicalizationError,
+    CanonicalizationError(#[from] CanonicalizationError),
 
     #[error("invalid encoding")]
     InvalidEncoding(#[from] base64::DecodeError),
@@ -48,11 +49,10 @@ pub fn get_json_signature(
     {
         return Err(VerificationError::InvalidProof("invalid proof"));
     };
-    let canon = serde_jcs::to_string(&object)
+    let message = canonicalize_object(&object)?;
-        .map_err(|_| VerificationError::CanonicalizationError)?;
     let signature_data = SignatureData {
         key_id: proof.verification_method,
-        message: canon,
+        message: message,
         signature: proof.proof_value,
     };
     Ok(signature_data)