1 files changed, 64 insertions, 0 deletions
diff --git a/packages/server/src/helpers/convertPublicKeyToPEM.ts b/packages/server/src/helpers/convertPublicKeyToPEM.ts
new file mode 100644
index 0000000..a7e04bd
--- /dev/null
+++ b/packages/server/src/helpers/convertPublicKeyToPEM.ts
@@ -0,0 +1,64 @@
+import cbor from 'cbor';
+import jwkToPem from 'jwk-to-pem';
+import base64url from 'base64url';
+
+import { COSEKEYS, COSEKTY, COSECRV } from './convertCOSEtoPKCS';
+
+export default function convertPublicKeyToPEM(publicKey: string): string {
+  const struct = cbor.decodeFirstSync(base64url.toBuffer(publicKey));
+
+  const kty = struct.get(COSEKEYS.kty);
+
+  if (!kty) {
+    throw new Error('Public key was missing kty');
+  }
+
+  if (kty === COSEKTY.EC2) {
+    const crv = struct.get(COSEKEYS.crv);
+    const x = struct.get(COSEKEYS.x);
+    const y = struct.get(COSEKEYS.y);
+
+    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)');
+    }
+
+    const ecPEM = jwkToPem({
+      kty: 'EC',
+      // Specify curve as "P-256" from "p256"
+      crv: COSECRV[crv as number].replace('p', 'P-'),
+      x: (x as Buffer).toString('base64'),
+      y: (y as Buffer).toString('base64'),
+    });
+
+    return ecPEM;
+  } else if (kty === COSEKTY.RSA) {
+    const n = struct.get(COSEKEYS.n);
+    const e = struct.get(COSEKEYS.e);
+
+    if (!n) {
+      throw new Error('Public key was missing n (RSA)');
+    }
+
+    if (!e) {
+      throw new Error('Public key was missing e (RSA)');
+    }
+
+    const rsaPEM = jwkToPem({
+      kty: 'RSA',
+      n: (n as Buffer).toString('base64'),
+      e: (e as Buffer).toString('base64'),
+    });
+
+    return rsaPEM;
+  }
+
+  throw new Error(`Could not convert public key type ${kty} to PEM`);
+}