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v1/curve25519.d

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+module angel.utils.cryptography.curve25519;
+
+import angel.utils.cryptography.fieldelem;
+import angel.utils.cryptography.utils;
+
+public enum ubyte[32] publicBasePoint = cast(immutable (ubyte[32]) ) x"0900000000000000000000000000000000000000000000000000000000000000";
+
+@safe nothrow @nogc:
+
+/// 
+/// 
+/// Params:
+/// secret = Your secret key, the 'exponent'.
+/// p = Receivers public key. Default base point = 9.
+/// 
+/// Returns: p^secret.
+/// 
+/// Examples:
+/// 
+/// ubyte[32] publicKey = curve25519_scalarmult(secretKey);
+/// 
+/// ubyte[32] sharedKey = curve25519_scalarmult(mySecretKey, herPublicKey);
+/// 
+ubyte[32] curve25519_scalarmult(
+	in ubyte[] secret, 
+	in ubyte[] p = cast(const ubyte[32]) publicBasePoint) @safe nothrow @nogc
+in {
+	assert(secret.length == 32, "Secret key must be 32 bytes long.");
+	assert(p.length == 32, "Public key must be 32 bytes long.");
+} body {
+	ubyte[32] sec = secret;
+	scope(exit) {
+		wipe(sec);
+	}
+
+	ubyte[32] pub = p;
+
+	return curve25519_scalarmult(sec, pub);
+}
+
+/// 
+/// 
+/// Params:
+/// secret = Your secret key, the 'exponent'.
+/// p = Receivers public key. Default base point = 9.
+/// 
+/// Returns: p^secret.
+/// 
+/// Examples:
+/// 
+/// ubyte[32] publicKey = curve25519_scalarmult(secretKey);
+/// 
+/// ubyte[32] sharedKey = curve25519_scalarmult(mySecretKey, herPublicKey);
+/// 
+ubyte[32] curve25519_scalarmult(in ref ubyte[32] secret, in ref ubyte[32] p = publicBasePoint) @safe nothrow @nogc
+{
+	ubyte[32] e = secret;
+	scope(exit) {
+		wipe(e);
+	}
+	clamp(e);
+
+	fe x1, x2, x3, z2, z3, tmp0, tmp1;
+	scope(exit) {
+		wipe(x1);
+		wipe(x2);
+		wipe(x3);
+		wipe(z2);
+		wipe(z3);
+		wipe(tmp0);
+		wipe(tmp1);
+	}
+
+	x1 = fe.fromBytes(p);
+	x2 = fe.one;
+	z2 = fe.zero;
+	x3 = x1;
+	z3 = fe.one;
+
+	uint swap = 0, b;
+	for (int pos = 254; pos >= 0;--pos) {
+		b = e[pos / 8] >> (pos & 7);
+		b &= 1;
+		swap ^= b;
+		fe_cswap(x2,x3,swap);
+		fe_cswap(z2,z3,swap);
+		swap = b;
+
+		tmp0 = x3 - z3;
+
+		tmp1 = x2 - z2;
+		x2 += z2;
+		z2 = x3 + z3;
+
+		z3 = tmp0 * x2;
+
+		z2 *= tmp1;
+		tmp0 = tmp1.sq;
+		tmp1 = x2.sq;
+		x3 = z2 + z3;
+
+		z2 = z3 - z2;
+		x2 = tmp0 * tmp1;
+
+		tmp1 -= tmp0;
+		
+		z2 = z2.sq;
+
+		z3 = fe_mul121666(tmp1);
+
+		x3 = x3.sq;
+
+		tmp0 += z3;
+		z3 = x1 * z2;
+
+		z2 = tmp0 * tmp1;
+	}
+	fe_cswap(x2,x3,swap);
+	fe_cswap(z2,z3,swap);
+
+	x2 *= z2.inverse;
+	return x2.toBytes;
+}
+
+/// Transforms 32 random bytes into a valid secret key.
+/// 
+/// Params:
+/// sk = 32 byte secret key.
+package void clamp(ubyte[] sk) pure
+in {
+	assert(sk.length == 32);
+} body {
+	sk[0] &= 248;
+	sk[31] &= 63;
+	sk[31] |= 64;
+}