Added generic PBKDF2 implementation.

lib/std/hash/hmac.c3

@@ -1,4 +1,5 @@
 module std::hash::hmac(<HashAlg, HASH_BYTES, BLOCK_BYTES>);
+import std::crypto;
 
 struct Hmac
 {
@@ -13,6 +14,34 @@ fn char[HASH_BYTES] hash(char[] key, char[] message)
 	return hmac.final();
 }
 
+/**
+ * @require output.len > 0 "Output must be greater than zero"
+ * @require output.len < int.max / HASH_BYTES "Output is too large"
+ **/
+fn void pbkdf2(char[] pw, char[] salt, uint iterations, char[] output)
+{
+	usz l = output.len / HASH_BYTES;
+	usz r = output.len % HASH_BYTES;
+
+	Hmac hmac;
+	hmac.init(pw);
+
+	char[] dst_curr = output;
+	for (usz i = 1; i <= l; i++)
+	{
+		@derive(&hmac, salt, iterations, i, dst_curr[:HASH_BYTES]);
+		dst_curr = dst_curr[HASH_BYTES..];
+	}
+
+	if (r > 0)
+	{
+		char[HASH_BYTES] tmp;
+		@derive(&hmac, salt, iterations, l + 1, &tmp);
+		dst_curr[..] = tmp[:dst_curr.len];
+		mem::zero_volatile(&tmp);
+	}
+}
+
 fn void Hmac.init(&self, char[] key)
 {
 	char[BLOCK_BYTES] buffer;
@@ -37,7 +66,7 @@ fn void Hmac.init(&self, char[] key)
 	self.b.init();
 	self.b.update(&buffer);
 
-	buffer = {};
+	mem::zero_volatile(&buffer);
 }
 
 fn void Hmac.update(&self, char[] data)
@@ -53,3 +82,26 @@ fn char[HASH_BYTES] Hmac.final(&self)
 
 const IPAD @private = 0x36;
 const OPAD @private = 0x5C;
+
+macro @derive(Hmac *hmac_start, char[] salt, uint iterations, usz index, char[] out)
+{
+	assert(out.len == HASH_BYTES);
+	char[HASH_BYTES] tmp @noinit;
+	defer mem::zero_volatile(&tmp);
+	Hmac hmac  = *hmac_start;
+	hmac.update(salt);
+	UIntBE be = { (uint)index };
+	hmac.update(&&bitcast(be, char[4]));
+	tmp = hmac.final();
+	out[..] = tmp;
+	for (int it = 1; it < iterations; it++)
+	{
+		hmac = *hmac_start;
+		hmac.update(&tmp);
+		tmp = hmac.final();
+		foreach (i, v : tmp)
+		{
+			out[i] ^= v;
+		}
+	}
+}