🔏 [FIX]: Trustchain "Expected signature to be an Uint8Array with leng…

…th 64" error (#7719)

* Test the verification of problematic signatures
From occasionaly returned from the Apdu device reponses

* Fix the "Expected signature to be an Uint8Array with length 64" error

* Update change log

* Keep `NobleCryptoSecp256k1.derDecode` private

---------

Co-authored-by: Theophile Sandoz <Theophile Sandoz>

.changeset/shaggy-crabs-approve.md

@@ -0,0 +1,5 @@
+---
+"@ledgerhq/hw-trustchain": patch
+---
+
+Fix the "Expected signature to be an Uint8Array with length 64" error

libs/hw-trustchain/src/NobleCrypto.ts

@@ -59,7 +59,10 @@ export class NobleCryptoSecp256k1 implements Crypto {
       6 + signature[3],
       6 + signature[3] + signature[5 + signature[3]],
     );
-    return { R: R.slice(R.length - PRIVATE_KEY_SIZE), S: S.slice(S.length - PRIVATE_KEY_SIZE) };
+    return {
+      R: this.enforceLength(R, PRIVATE_KEY_SIZE),
+      S: this.enforceLength(S, PRIVATE_KEY_SIZE),
+    };
   }
 
   async sign(message: Uint8Array, keyPair: KeyPair): Promise<Uint8Array> {
@@ -105,6 +108,19 @@ export class NobleCryptoSecp256k1 implements Crypto {
     return c;
   }
 
+  private enforceLength(buffer: Uint8Array, length: number): Uint8Array {
+    if (buffer.length > length) {
+      return buffer.slice(buffer.length - length); // truncate extra bytes from the start
+    } else if (buffer.length < length) {
+      const padded = new Uint8Array(length);
+      const start = length - buffer.length;
+      padded.set(Array(start).fill(0));
+      padded.set(buffer, start);
+      return padded;
+    }
+    return buffer;
+  }
+
   private pad(message: Uint8Array): Uint8Array {
     // ISO9797M2 implementation
     const padLength = AES_BLOCK_SIZE - (message.length % AES_BLOCK_SIZE);

libs/hw-trustchain/src/__tests__/crypto.ts

@@ -27,4 +27,18 @@ describe("Sodium wrapper tester", () => {
     const decrypted = await crypto.decryptUserData(keypair.privateKey, encrypted);
     expect(crypto.to_hex(decrypted)).toBe(crypto.to_hex(data));
   });
+
+  it("should verify truncated signature by padding 0s from the start", async () => {
+    const hash = crypto.from_hex(
+      "19514a2e50bfad4a6de397ebde776191cbb720e8bbfcc3c165385c3664c03341",
+    );
+    const signature = crypto.from_hex(
+      // Here the "S" part of the signature is only 31 bytes long it should be padded with a 0
+      "3043022052a82876fcd4d9d8383ce12a7e4d96bb4c1d9e71e857cd087c092b87cec6baeb021f6b86b9a3bab1e7794ca6ef081c66cb6e6dff06cceddbd23e1f25089e311784",
+    );
+    const issuer = crypto.from_hex(
+      "026e7bf1e015da491674be5796b15d6fabd1f454aad478a6a223934e5a872719e0",
+    );
+    expect(await crypto.verify(hash, signature, issuer)).toBe(true);
+  });
 });