From a9252c66497ba33e63ce08cc942e4d680a02835f Mon Sep 17 00:00:00 2001
From: Dan Habot <dan.habot@gmail.com>
Date: Wed, 16 Jun 2021 05:46:49 -0400
Subject: [PATCH] Add Signature#getSigningKeyIDs method to get Issuer Key IDs
 from a Signature (#1331)

---
 openpgp.d.ts              |  1 +
 src/signature.js          | 13 +++++++++++++
 test/general/signature.js | 24 ++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/openpgp.d.ts b/openpgp.d.ts
index cf8f1d12..6f23bea2 100644
--- a/openpgp.d.ts
+++ b/openpgp.d.ts
@@ -114,6 +114,7 @@ export class Signature {
   constructor(packetlist: PacketList<SignaturePacket>);
   public write(): MaybeStream<Uint8Array>;
   public armor(config?: Config): string;
+  public getSigningKeyIDs(): Array<KeyID>;
 }
 
 interface VerificationResult {
diff --git a/src/signature.js b/src/signature.js
index 9b64887e..b50b6262 100644
--- a/src/signature.js
+++ b/src/signature.js
@@ -51,6 +51,19 @@ export class Signature {
   armor(config = defaultConfig) {
     return armor(enums.armor.signature, this.write(), undefined, undefined, undefined, config);
   }
+
+  /**
+   * Returns an array of KeyIDs of all of the issuers who created this signature
+   * @returns {Array<KeyID>} The Key IDs of the signing keys
+   */
+  getSigningKeyIDs() {
+    const keyIDs = [];
+    const signatureList = this.packets.filterByTag(enums.packet.signature);
+    signatureList.forEach(function(packet) {
+      keyIDs.push(packet.issuerKeyID);
+    });
+    return keyIDs;
+  }
 }
 
 /**
diff --git a/test/general/signature.js b/test/general/signature.js
index 376df8d6..a265a73f 100644
--- a/test/general/signature.js
+++ b/test/general/signature.js
@@ -650,6 +650,30 @@ hUhMKMuiM3pRwdIyDOItkUWQmjEEw7/XmhgInkXsCw==
 -----END PGP SIGNATURE-----
 `;
 
+  it("Retrieve the issuer Key ID of a signature", async function () {
+    const { privateKeyArmored, publicKeyArmored } = await openpgp.generateKey({
+      type: "ecc", // Type of the key, defaults to ECC
+      curve: "curve25519", // ECC curve name, defaults to curve25519
+      userIDs: [{ name: "name", email: "test@email.com" }], // you can pass multiple user IDs
+      passphrase: "password" // protects the private key
+    });
+
+    const publicKey = await openpgp.readKey({ armoredKey: publicKeyArmored });
+    const privateKey = await openpgp.decryptKey({
+      privateKey: await openpgp.readKey({ armoredKey: privateKeyArmored }),
+      passphrase: "password"
+    });
+    const message = await openpgp.createMessage({ text: "test" });
+    const armoredSignature = await openpgp.sign({
+      message,
+      signingKeys: privateKey,
+      detached: true
+    });
+    const signature = await openpgp.readSignature({ armoredSignature });
+    expect(signature.getSigningKeyIDs).to.exist;
+    expect(signature.getSigningKeyIDs().map(x => x.toHex())).to.include(publicKey.getKeyID().toHex());
+  });
+
   it('Throws when reading a signature missing the creation time', async function () {
     const armoredSignature = `-----BEGIN PGP SIGNATURE-----