diff --git a/src/core/operations/KeyToExtendedKey.mjs b/src/core/operations/KeyToExtendedKey.mjs
new file mode 100644
index 00000000..b5b168b2
--- /dev/null
+++ b/src/core/operations/KeyToExtendedKey.mjs
@@ -0,0 +1,87 @@
+/**
+ * @author dcgoldenberg [dgoldenberg@mitre.org]
+ * @copyright Crown Copyright 2025
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import OperationError from "../errors/OperationError.mjs";
+import { makeSureIsHex,  serializeExtendedKeyFunc, getExtendedKeyVersion } from "../lib/Bitcoin.mjs";
+
+
+/**
+ * Key To Extended Key operation
+ */
+class KeyToExtendedKey extends Operation {
+
+    /**
+     * KeyToExtendedKey constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "Key To Extended Key";
+        this.module = "Default";
+        this.description = "Turns a key, with chaincode and version as parameters, into an extended key. We assume the key is meant to be a master key, so depth and child number are set to 0, and fingerprint is set to 00000000.";
+        this.infoURL = "https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki"; // 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": "Chaincode",
+                "type": "toggleString",
+                "value": "",
+                "toggleValues": ["Hex"]
+            },
+            {
+                "name": "Version Type",
+                "type": "option",
+                "value": ["xpub", "xprv", "ypub", "yprv", "zpub", "zprv", "Zpub", "Zprv", "Ypub", "Yprv", "Ltub", "Ltpv", "Mtub", "Mtpv", "ttub", "ttpv", "tpub", "tprv", "upub", "uprv", "vpub", "vprv", "Upub", "Uprv", "Vpub", "Vprv"]
+            }
+            /* Example arguments. See the project wiki for full details.
+            {
+                name: "First arg",
+                type: "string",
+                value: "Don't Panic"
+            },
+            {
+                name: "Second arg",
+                type: "number",
+                value: 42
+            }
+            */
+        ];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    run(input, args) {
+        // const [firstArg, secondArg] = args;
+
+        const inputAsHex = makeSureIsHex(input);
+        const isPublic = inputAsHex.length === 66 && (inputAsHex.startsWith("03") || inputAsHex.startsWith("02"));
+        const isPrivate = inputAsHex.length === 64;
+        const privateVersions = ["xprv",  "yprv",  "zprv",  "Zprv",  "Yprv",  "Ltpv",  "Mtpv",  "ttpv", "tprv",  "uprv",  "vprv",  "Uprv", "Vprv"];
+        if (!isPublic && !isPrivate) {
+            throw new OperationError("Error: String " + inputAsHex + " is not a valid public or private key.");
+        }
+        if (isPublic && privateVersions.indexOf(args[1]) !== -1) {
+            throw new OperationError("Error: Mis-Match between version and key type. Public Key is entered, but a private version is selected.");
+        }
+        if (isPrivate && privateVersions.indexOf(args[1]) === -1) {
+            throw new OperationError("Error: Mis-Match between version and key type. Private Key is entered, but a public version is selected.");
+        }
+        const key =  isPrivate ? "00" + inputAsHex : inputAsHex;
+        const newVersion = getExtendedKeyVersion(args[1]);
+
+        const newExtendedKey = serializeExtendedKeyFunc(newVersion, 0, "00000000", 0, args[0].string, key);
+        return newExtendedKey;
+
+    }
+
+}
+
+export default KeyToExtendedKey;
diff --git a/tests/operations/tests/KeyToExtendedKey.mjs b/tests/operations/tests/KeyToExtendedKey.mjs
new file mode 100644
index 00000000..cfb532b6
--- /dev/null
+++ b/tests/operations/tests/KeyToExtendedKey.mjs
@@ -0,0 +1,82 @@
+/**
+ * Key To Extended Key Tests.
+ *
+ * @author dgoldenberg [virtualcurrency@mitre.org]
+ * @copyright  MITRE 2023
+ * @license Apache-2.0
+ */
+
+import TestRegister from "../../lib/TestRegister.mjs";
+
+
+TestRegister.addTests([
+    {
+        name: "Key To Extended Key (Basic, XPRV)",
+        input: "f55acd736ff0f80f2cdc56ab5ac1e4d4ce92e1f46d137a282a61e706681df9c5",
+        expectedOutput: "xprv9s21ZrQH143K4bXtdSLbsWGSfAok775A1bF3YwPeHe8ePa7QwD5V4kK1RmdZV2M6TKVfszKt19UaHfyqdQ2MZ8dv2t7G2Tvtxnef7Pxu8Qu",
+        recipeConfig: [
+            {
+                "op": "Key To Extended Key",
+                "args": [
+                    {
+                        "option": "Hex",
+                        "string": "fedf6c5ebcc2fc7b66291e55501a005886128bf97aeced3a91478a0c44f54dbe"
+                    },
+                    "xprv"
+                ]
+            }
+        ],
+    },
+    {
+        name: "Key To Extended Key (YPRV Same Data)",
+        input: "f55acd736ff0f80f2cdc56ab5ac1e4d4ce92e1f46d137a282a61e706681df9c5",
+        expectedOutput: "yprvABrGsX5C9janutj1To8E5bMwq8xC3j4evhmGLLHXfeWXSfveBsF3goy9Syb9Uw11rxcUdTvSToq8AxbQM6SNMNKWuDogcNkPEWiJVuszXFR",
+        recipeConfig: [
+            {
+                "op": "Key To Extended Key",
+                "args": [
+                    {
+                        "option": "Hex",
+                        "string": "fedf6c5ebcc2fc7b66291e55501a005886128bf97aeced3a91478a0c44f54dbe"
+                    },
+                    "yprv"
+                ]
+            }
+        ],
+    },
+    {
+        name: "Key To Extended Key (Public Key With Private Version), Should Throw Error.",
+        input: "02233f618dad285dc8b03eb7bf9a59dec039b7c1b2433dabdca636e17e10890e85",
+        expectedOutput: "Error: Mis-Match between version and key type. Public Key is entered, but a private version is selected.",
+        recipeConfig: [
+            {
+                "op": "Key To Extended Key",
+                "args": [
+                    {
+                        "option": "Hex",
+                        "string": "cda6685894f356bdf1bd6af6cb7e3961e550fb9c9b2c82d9ebfd89f48c2afea6"
+                    },
+                    "xprv"
+                ]
+            }
+        ],
+    },
+    {
+        name: "Key To Extended Key (Private Key With Public Version), Should Throw Error.",
+        input: "f55acd736ff0f80f2cdc56ab5ac1e4d4ce92e1f46d137a282a61e706681df9c5",
+        expectedOutput: "Error: Mis-Match between version and key type. Private Key is entered, but a public version is selected.",
+        recipeConfig: [
+            {
+                "op": "Key To Extended Key",
+                "args": [
+                    {
+                        "option": "Hex",
+                        "string": "fedf6c5ebcc2fc7b66291e55501a005886128bf97aeced3a91478a0c44f54dbe"
+                    },
+                    "xpub"
+                ]
+            }
+        ],
+    },
+
+]);