ChaChaWith64BitNonce

fn ChaChaWith64BitNonce(comptime rounds_nb: usize) type

File

Code

fn ChaChaWith64BitNonce(comptime rounds_nb: usize) type {
    return struct {
        /// Nonce length in bytes.
        pub const nonce_length = 8;
        /// Key length in bytes.
        pub const key_length = 32;
        /// Block length in bytes.
        pub const block_length = 64;

        /// Add the output of the ChaCha20 stream cipher to `in` and stores the result into `out`.
        /// WARNING: This function doesn't provide authenticated encryption.
        /// Using the AEAD or one of the `box` versions is usually preferred.
        pub fn xor(out: []u8, in: []const u8, counter: u64, key: [key_length]u8, nonce: [nonce_length]u8) void {
            assert(in.len == out.len);
            assert(in.len <= 64 * (@as(u71, 1 << 64) - counter));

            const k = keyToWords(key);
            var c: [4]u32 = undefined;
            c[0] = @truncate(counter);
            c[1] = @truncate(counter >> 32);
            c[2] = mem.readInt(u32, nonce[0..4], .little);
            c[3] = mem.readInt(u32, nonce[4..8], .little);
            ChaChaImpl(rounds_nb).chacha20Xor(out, in, k, c, true);
        }

        /// Write the output of the ChaCha20 stream cipher into `out`.
        pub fn stream(out: []u8, counter: u64, key: [key_length]u8, nonce: [nonce_length]u8) void {
            assert(out.len <= 64 * (@as(u71, 1 << 64) - counter));

            const k = keyToWords(key);
            var c: [4]u32 = undefined;
            c[0] = @truncate(counter);
            c[1] = @truncate(counter >> 32);
            c[2] = mem.readInt(u32, nonce[0..4], .little);
            c[3] = mem.readInt(u32, nonce[4..8], .little);
            ChaChaImpl(rounds_nb).chacha20Stream(out, k, c, true);
        }
    };
}