1 files changed, 115 insertions, 0 deletions
diff --git a/packages/server/src/helpers/iso/isoCrypto/verifyEC2.ts b/packages/server/src/helpers/iso/isoCrypto/verifyEC2.ts
new file mode 100644
index 0000000..9e91d3e
--- /dev/null
+++ b/packages/server/src/helpers/iso/isoCrypto/verifyEC2.ts
@@ -0,0 +1,115 @@
+import { webcrypto } from 'node:crypto';
+import { ECDSASigValue } from "@peculiar/asn1-ecc";
+import { AsnParser } from '@peculiar/asn1-schema';
+
+import { COSEALG, COSECRV, COSEKEYS, COSEPublicKeyEC2 } from "../../cose";
+import { mapCoseAlgToWebCryptoAlg } from "./mapCoseAlgToWebCryptoAlg";
+import { importKey } from './importKey';
+import { isoBase64URL, isoUint8Array } from '../index';
+import { SubtleCryptoCrv } from "./structs";
+
+/**
+ * Verify a signature using an EC2 public key
+ */
+export async function verifyEC2(opts: {
+  cosePublicKey: COSEPublicKeyEC2,
+  signature: Uint8Array,
+  data: Uint8Array,
+  shaHashOverride?: COSEALG,
+}): Promise<boolean> {
+  const { cosePublicKey, signature, data, shaHashOverride } = opts;
+
+  // The signature is wrapped in ASN.1 structure, so we need to peel it apart
+  const parsedSignature = AsnParser.parse(signature, ECDSASigValue);
+  let rBytes = new Uint8Array(parsedSignature.r);
+  let sBytes = new Uint8Array(parsedSignature.s);
+
+  if (shouldRemoveLeadingZero(rBytes)) {
+    rBytes = rBytes.slice(1);
+  }
+
+  if (shouldRemoveLeadingZero(sBytes)) {
+    sBytes = sBytes.slice(1);
+  }
+
+  const finalSignature = isoUint8Array.concat([rBytes, sBytes]);
+
+  // Import the public key
+  const alg = cosePublicKey.get(COSEKEYS.alg);
+  const crv = cosePublicKey.get(COSEKEYS.crv);
+  const x = cosePublicKey.get(COSEKEYS.x);
+  const y = cosePublicKey.get(COSEKEYS.y);
+
+  if (!alg) {
+    throw new Error('Public key was missing alg (EC2)');
+  }
+
+  if (!crv) {
+    throw new Error('Public key was missing crv (EC2)');
+  }
+
+  if (!x) {
+    throw new Error('Public key was missing x (EC2)');
+  }
+
+  if (!y) {
+    throw new Error('Public key was missing y (EC2)');
+  }
+
+  let _crv: SubtleCryptoCrv;
+  if (crv === COSECRV.P256) {
+    _crv = 'P-256';
+  } else if (crv === COSECRV.P384) {
+    _crv = 'P-384';
+  } else if (crv === COSECRV.P521) {
+    _crv = 'P-521';
+  } else {
+    throw new Error(`Unexpected COSE crv value of ${crv}`);
+  }
+
+  const keyData: JsonWebKey = {
+    kty: "EC",
+    crv: _crv,
+    x: isoBase64URL.fromBuffer(x),
+    y: isoBase64URL.fromBuffer(y),
+    ext: false,
+  };
+
+  const keyAlgorithm: EcKeyImportParams = {
+    name: 'ECDSA',
+    namedCurve: _crv,
+  };
+
+  const key = await importKey({
+    keyData,
+    algorithm: keyAlgorithm,
+  });
+
+  // Determine which SHA algorithm to use for signature verification
+  let subtleAlg = mapCoseAlgToWebCryptoAlg(alg);
+  if (shaHashOverride) {
+    subtleAlg = mapCoseAlgToWebCryptoAlg(shaHashOverride);
+  }
+
+  const verifyAlgorithm: EcdsaParams = {
+    name: 'ECDSA',
+    hash: { name: subtleAlg },
+  };
+
+  if (globalThis.crypto) {
+    return globalThis.crypto.subtle.verify(verifyAlgorithm, key, finalSignature, data);
+  } else {
+    return webcrypto.subtle.verify(verifyAlgorithm, key, finalSignature, data);
+  }
+}
+
+/**
+ * Determine if the DER-specific `00` byte at the start of an ECDSA signature byte sequence
+ * should be removed based on the following logic:
+ *
+ * "If the leading byte is 0x0, and the the high order bit on the second byte is not set to 0,
+ * then remove the leading 0x0 byte"
+ */
+function shouldRemoveLeadingZero(bytes: Uint8Array): boolean {
+  return (bytes[0] === 0x0 && (bytes[1] & (1 << 7)) !== 0);
+}