crypto: remove default encoding from DiffieHellman

getDefaultEncoding() always returns 'buffer' in Node.js 20.

In diffiehellman.js, this value is always used as input to either
toBuf(), encode(), or getArrayBufferOrView(). All of these functions
treat any falsy encoding just like 'buffer', so we can safely remove the
calls to getDefaultEncoding().

Refs: nodejs#47182

lib/internal/crypto/diffiehellman.js

@@ -51,7 +51,6 @@ const {
 
 const {
   getArrayBufferOrView,
-  getDefaultEncoding,
   jobPromise,
   toBuf,
   kHandle,
@@ -97,10 +96,6 @@ function DiffieHellman(sizeOrKey, keyEncoding, generator, genEncoding) {
     keyEncoding = false;
   }
 
-  const encoding = getDefaultEncoding();
-  keyEncoding = keyEncoding || encoding;
-  genEncoding = genEncoding || encoding;
-
   if (typeof sizeOrKey !== 'number')
     sizeOrKey = toBuf(sizeOrKey, keyEncoding);
 
@@ -148,7 +143,6 @@ DiffieHellmanGroup.prototype.generateKeys =
 
 function dhGenerateKeys(encoding) {
   const keys = this[kHandle].generateKeys();
-  encoding = encoding || getDefaultEncoding();
   return encode(keys, encoding);
 }
 
@@ -158,9 +152,6 @@ DiffieHellmanGroup.prototype.computeSecret =
     dhComputeSecret;
 
 function dhComputeSecret(key, inEnc, outEnc) {
-  const encoding = getDefaultEncoding();
-  inEnc = inEnc || encoding;
-  outEnc = outEnc || encoding;
   key = getArrayBufferOrView(key, 'key', inEnc);
   const ret = this[kHandle].computeSecret(key);
   if (typeof ret === 'string')
@@ -175,7 +166,6 @@ DiffieHellmanGroup.prototype.getPrime =
 
 function dhGetPrime(encoding) {
   const prime = this[kHandle].getPrime();
-  encoding = encoding || getDefaultEncoding();
   return encode(prime, encoding);
 }
 
@@ -186,7 +176,6 @@ DiffieHellmanGroup.prototype.getGenerator =
 
 function dhGetGenerator(encoding) {
   const generator = this[kHandle].getGenerator();
-  encoding = encoding || getDefaultEncoding();
   return encode(generator, encoding);
 }
 
@@ -197,7 +186,6 @@ DiffieHellmanGroup.prototype.getPublicKey =
 
 function dhGetPublicKey(encoding) {
   const key = this[kHandle].getPublicKey();
-  encoding = encoding || getDefaultEncoding();
   return encode(key, encoding);
 }
 
@@ -208,21 +196,18 @@ DiffieHellmanGroup.prototype.getPrivateKey =
 
 function dhGetPrivateKey(encoding) {
   const key = this[kHandle].getPrivateKey();
-  encoding = encoding || getDefaultEncoding();
   return encode(key, encoding);
 }
 
 
 DiffieHellman.prototype.setPublicKey = function setPublicKey(key, encoding) {
-  encoding = encoding || getDefaultEncoding();
   key = getArrayBufferOrView(key, 'key', encoding);
   this[kHandle].setPublicKey(key);
   return this;
 };
 
 
 DiffieHellman.prototype.setPrivateKey = function setPrivateKey(key, encoding) {
-  encoding = encoding || getDefaultEncoding();
   key = getArrayBufferOrView(key, 'key', encoding);
   this[kHandle].setPrivateKey(key);
   return this;
@@ -251,15 +236,12 @@ ECDH.prototype.generateKeys = function generateKeys(encoding, format) {
 ECDH.prototype.getPublicKey = function getPublicKey(encoding, format) {
   const f = getFormat(format);
   const key = this[kHandle].getPublicKey(f);
-  encoding = encoding || getDefaultEncoding();
   return encode(key, encoding);
 };
 
 ECDH.convertKey = function convertKey(key, curve, inEnc, outEnc, format) {
   validateString(curve, 'curve');
-  const encoding = inEnc || getDefaultEncoding();
-  key = getArrayBufferOrView(key, 'key', encoding);
-  outEnc = outEnc || encoding;
+  key = getArrayBufferOrView(key, 'key', inEnc);
   const f = getFormat(format);
   const convertedKey = _ECDHConvertKey(key, curve, f);
   return encode(convertedKey, outEnc);