Public Key from Private Key

src/core/operations/PubKeyFromPrivKey.mjs

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+/**
+ * @author cplussharp
+ * @copyright Crown Copyright 2023
+ * @license Apache-2.0
+ */
+
+import r from "jsrsasign";
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+
+/**
+ * Public Key from Private Key operation
+ */
+class PubKeyFromPrivKey extends Operation {
+
+    /**
+     * PubKeyFromPrivKey constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Public Key from Private Key";
+        this.module = "PublicKey";
+        this.description = "Extracts the Public Key from a Private Key.";
+        this.infoURL = "https://en.wikipedia.org/wiki/PKCS_8";
+        this.inputType = "string";
+        this.outputType = "string";
+        this.args = [];
+        this.checks = [];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    run(input, args) {
+        let output = "";
+        let match;
+        const regex = /-----BEGIN ((RSA |EC |DSA )?PRIVATE KEY)-----/g;
+        while ((match = regex.exec(input)) !== null) {
+            // find corresponding end tag
+            const indexBase64 = match.index + match[0].length;
+            const footer = `-----END ${match[1]}-----`;
+            const indexFooter = input.indexOf(footer, indexBase64);
+            if (indexFooter === -1) {
+                throw new OperationError(`PEM footer '${footer}' not found`);
+            }
+
+            const privKeyPem = input.substring(match.index, indexFooter + footer.length);
+            let privKey;
+            try {
+                privKey = r.KEYUTIL.getKey(privKeyPem);
+            } catch (err) {
+                throw new OperationError(`Unsupported key type: ${err}`);
+            }
+            let pubKey;
+            if (privKey.type && privKey.type === "EC") {
+                pubKey = new r.KJUR.crypto.ECDSA({ curve: privKey.curve });
+                pubKey.setPublicKeyHex(privKey.generatePublicKeyHex());
+            } else if (privKey.type && privKey.type === "DSA") {
+                if (!privKey.y) {
+                    throw new OperationError(`DSA Private Key in PKCS#8 is not supported`);
+                }
+                pubKey = new r.KJUR.crypto.DSA();
+                pubKey.setPublic(privKey.p, privKey.q, privKey.g, privKey.y);
+            } else if (privKey.n && privKey.e) {
+                pubKey = new r.RSAKey();
+                pubKey.setPublic(privKey.n, privKey.e);
+            } else {
+                throw new OperationError(`Unsupported key type`);
+            }
+            const pubKeyPem = r.KEYUTIL.getPEM(pubKey);
+
+            // PEM ends with '\n', so a new key always starts on a new line
+            output += pubKeyPem;
+        }
+        return output;
+    }
+}
+
+export default PubKeyFromPrivKey;