Add PGP Sign (only) operation

src/core/config/Categories.json

@@ -188,6 +188,7 @@
             "Generate PGP Key Pair",
             "PGP Encrypt",
             "PGP Decrypt",
+            "PGP Sign",
             "PGP Verify",
             "PGP Encrypt and Sign",
             "PGP Decrypt and Verify",

src/core/operations/PGPSign.mjs

@@ -0,0 +1,83 @@
+/**
+ * @author GCHQDeveloper581
+ * @copyright Crown Copyright 2026
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import kbpgp from "kbpgp";
+import { ASP, importPrivateKey } from "../lib/PGP.mjs";
+import OperationError from "../errors/OperationError.mjs";
+import * as es6promisify from "es6-promisify";
+const promisify = es6promisify.default ? es6promisify.default.promisify : es6promisify.promisify;
+
+/**
+ * PGP Sign operation
+ */
+class PGPSign extends Operation {
+
+    /**
+     * PGPSign constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "PGP Sign";
+        this.module = "PGP";
+        this.description = [
+            "Input: the message you want to sign",
+            "<br><br>",
+            "Arguments: the ASCII-armoured PGP private key of the sender.",
+            "<br><br>",
+            "Pretty Good Privacy is an encryption standard (OpenPGP) used for encrypting, decrypting, and signing messages.",
+            "<br><br>",
+            "This function uses the Keybase implementation of PGP.",
+        ].join("\n");
+        this.infoURL = "https://wikipedia.org/wiki/Pretty_Good_Privacy"; // Usually a Wikipedia link. Remember to remove localisation (i.e. https://wikipedia.org/etc rather than https://en.wikipedia.org/etc)
+        this.inputType = "string";
+        this.outputType = "string";
+        this.args = [
+            {
+                "name": "Private key of signer",
+                "type": "text",
+                "value": ""
+            },
+            {
+                "name": "Private key passphrase (optional)",
+                "type": "string",
+                "value": ""
+            }
+        ];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     *
+     * @throws {OperationError} if failed private key import or failed encryption
+     */
+    async run(input, args) {
+        const message = input,
+            [privateKey, passphrase] = args;
+        let signedMessage;
+
+        if (!privateKey) throw new OperationError("Enter the private key of the signer.");
+        const privKey = await importPrivateKey(privateKey, passphrase);
+
+        try {
+            signedMessage = await promisify(kbpgp.box)({
+                "msg": message,
+                "sign_with": privKey,
+                "asp": ASP
+            });
+        } catch (err) {
+            throw new OperationError(`Couldn't sign message: ${err}`);
+        }
+
+        return signedMessage;
+    }
+
+}
+
+export default PGPSign;