Figure out Zig generics for GCM.

src/error.zig

@@ -2,4 +2,6 @@ pub const CryptoError = error{
     MessageLengthLimitExceeded,
     BufferSizeMismatch,
     InvalidIVLength,
+    InvalidTagLength,
+    IncorrectAuthenticationTag,
 };

src/primitive/blockcipher/mode_gcm.zig

@@ -1,44 +1,75 @@
 const std = @import("std");
+const testing = std.testing;
 
-const CryptoError = @import("../../error.zig").CryptoError;
+const CryptoError = error{
-
+    MessageLengthLimitExceeded,
-const Gcm128Ctx = struct {
+    BufferSizeMismatch,
-    const BLOCK_SIZE = 128 / 8;
+    InvalidIVLength,
-
+    InvalidTagLength,
-    cipher_key_size: comptime_int,
+    IncorrectAuthenticationTag,
-    cipher_encrypt_fn: fn (*const [.cipher_key_size]u8, *const [BLOCK_SIZE]u8, *[BLOCK_SIZE]u8) void,
-    key: [.cipher_key_size]u8,
-    counter: [BLOCK_SIZE]u8,
-    ghash_x: [BLOCK_SIZE]u8,
-    text_buffer: [BLOCK_SIZE]u8,
-    text_length: u64,
-    aad_length: u64,
 };
 
+pub const GCM_128_BLOCK_SIZE = 128 / 8;
+
+pub fn gcm_128_cipher_fn_t(comptime key_size: usize) type {
+    return fn (
+        key: *const [key_size]u8,
+        block_in: *const [GCM_128_BLOCK_SIZE]u8,
+        block_out: *[GCM_128_BLOCK_SIZE]u8,
+    ) void;
+}
+
+fn Gcm128Ctx(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+) type {
+    return struct {
+        const BLOCK_SIZE = GCM_128_BLOCK_SIZE;
+        const AAD_MAX_BYTES = (1 << 64) / 8;
+        const TEXT_MAX_BYTES = ((1 << 39) - 256) / 8;
+        const TAG_MAX_BYTES = 128 / 8;
+
+        const KEY_SIZE = cipher_key_size;
+        const CIPHER_FN = cipher_encrypt_fn;
+
+        key: [cipher_key_size]u8,
+        keystream: [BLOCK_SIZE]u8,
+        counter: [BLOCK_SIZE]u8,
+        ghash_x: [BLOCK_SIZE]u8,
+        h: [BLOCK_SIZE]u8,
+        ciphertext_buffer: [BLOCK_SIZE]u8,
+        ciphertext_length: u64,
+        aad_length: u64,
+    };
+}
+
 pub fn gcm_128_new(
-    cipher_key_size: comptime_int,
+    comptime cipher_key_size: usize,
-    cipher_encrypt_fn: fn (key: *const [cipher_key_size]u8, block_in: *const [Gcm128Ctx.BLOCK_SIZE]u8, block_out: *[Gcm128Ctx.BLOCK_SIZE]u8) void,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
     key: *const [cipher_key_size]u8,
     iv: []const u8,
-) Gcm128Ctx {
+) !Gcm128Ctx(cipher_key_size, cipher_encrypt_fn) {
     if (iv.len == 0) {
         return CryptoError.InvalidIVLength;
     }
 
-    var ctx = Gcm128Ctx{
+    var ctx = Gcm128Ctx(cipher_key_size, cipher_encrypt_fn){
-        .cipher_key_size = cipher_key_size,
-        .cipher_encrypt_fn = cipher_encrypt_fn,
         .key = undefined,
+        .keystream = undefined,
         .counter = undefined,
         .ghash_x = undefined,
-        .text_buffer = undefined,
+        .h = undefined,
-        .text_length = 0,
+        .ciphertext_buffer = undefined,
+        .ciphertext_length = 0,
         .aad_length = 0,
     };
 
     // Set the encryption/decryption key.
     @memcpy(&ctx.key, key);
 
+    // Compute the `H` value.
+    cipher_encrypt_fn(&ctx.key, &std.mem.zeroes([GCM_128_BLOCK_SIZE]u8), &ctx.h);
+
     // Set the counter initial value (`Y_0`).
     if (iv.len == 96 / 8) {
         @memcpy(ctx.counter[0 .. 96 / 8], iv);
@@ -51,7 +82,11 @@ pub fn gcm_128_new(
     return ctx;
 }
 
-pub fn gcm_128_destroy(ctx: *Gcm128Ctx) void {
+pub fn gcm_128_destroy(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
+) void {
     @memset(&ctx, 0);
 }
 
@@ -59,90 +94,242 @@ pub fn gcm_128_destroy(ctx: *Gcm128Ctx) void {
 // AFTER the context is initialized but BEFORE any data is en/decrypted.
 // TODO: Enforce at API level.
 pub fn gcm_128_authenticate_data_once(
-    ctx: *Gcm128Ctx,
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
     data: []const u8,
 ) !void {
     // The maximum bit length of the AAD is 2^64.
-    if (data.len > (1 << 61))
+    if (data.len >= Gcm128Ctx.AAD_MAX_BYTES)
         return CryptoError.MessageLengthLimitExceeded;
 
-    // Compute `H` temporarily.
-    const h = std.mem.zeroes([Gcm128Ctx.BLOCK_SIZE]u8);
-    ctx.cipher_encrypt_fn(&ctx.key, &h, &h);
-
-    // Since `H` depends on the key, destroy it before leaving the function.
-    defer @memset(&h, 0);
-
     // Compute and store `X_m` where m is the length in blocks of the AAD.
-    gcm_128_ghash_padded_chunk(&std.mem.zeroes([]u8), &h, data, &ctx.ghash_x);
+    gcm_128_ghash_padded_chunk(&std.mem.zeroes([]u8), &ctx.h, data, &ctx.ghash_x);
 
     // Store the AAD length for the tag computation.
     ctx.aad_length = data.len;
 }
 
-pub fn gcm_128_encrypt(ctx: *Gcm128Ctx, plaintext: []const u8, ciphertext: []u8) void {
+pub fn gcm_128_encrypt(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
+    plaintext: []const u8,
+    ciphertext: []u8,
+) !void {
     if (plaintext.len != ciphertext.len)
         return CryptoError.BufferSizeMismatch;
 
-    // TODO
+    if (ctx.ciphertext_length + plaintext.len >= @TypeOf(ctx.*).TEXT_MAX_BYTES)
-    _ = .{ ctx, plaintext, ciphertext };
+        return CryptoError.MessageLengthLimitExceeded;
+
+    const BS = GCM_128_BLOCK_SIZE;
+    var bytes_processed: usize = 0;
+
+    const bytes_buffered_ct = ctx.ciphertext_length % BS;
+
+    // If we're not at the beginning of a new block, use the existing keystream to encrypt the plaintext.
+    if (bytes_buffered_ct != 0) {
+        // Simplest case - no block border is reached - just XOR-encrypt and we're done.
+        if (bytes_buffered_ct + plaintext.len < BS) {
+            gcm_128_crypt_xor(
+                @TypeOf(ctx.*).KEY_SIZE,
+                @TypeOf(ctx.*).CIPHER_FN,
+                ctx,
+                plaintext,
+                ciphertext,
+                false,
+            );
+            return;
+        }
+        // Otherwise, encrypt the remainder of the block with the existing
+        // keystream and then authenticate the completed ciphertext block.
+        else {
+            gcm_128_crypt_xor(
+                @TypeOf(ctx.*).KEY_SIZE,
+                @TypeOf(ctx.*).CIPHER_FN,
+                ctx,
+                plaintext[0 .. BS - bytes_buffered_ct],
+                ciphertext[0 .. BS - bytes_buffered_ct],
+                false,
+            );
+            gcm_128_authenticate_ciphertext_block(
+                @TypeOf(ctx.*).KEY_SIZE,
+                @TypeOf(ctx.*).CIPHER_FN,
+                ctx,
+            );
+            bytes_processed += BS - bytes_buffered_ct;
+        }
     }
 
-pub fn gcm_128_encrypt_final(ctx: *Gcm128Ctx, tag_length: u4, tag: []u8) void {
+    // As long as we have another whole block worth of plaintext, encrypt it
-    // TODO
+    // and authenticate the CT.
-    _ = .{ ctx, tag_length, tag };
+    while ((plaintext.len - bytes_processed) / BS > 0) : (bytes_processed += BS) {
+        gcm_128_update_keystream(
+            @TypeOf(ctx.*).KEY_SIZE,
+            @TypeOf(ctx.*).CIPHER_FN,
+            ctx,
+        );
+        gcm_128_crypt_xor(
+            @TypeOf(ctx.*).KEY_SIZE,
+            @TypeOf(ctx.*).CIPHER_FN,
+            ctx,
+            plaintext[bytes_processed .. bytes_processed + BS],
+            ciphertext[bytes_processed .. bytes_processed + BS],
+            false,
+        );
+        gcm_128_authenticate_ciphertext_block(
+            @TypeOf(ctx.*).KEY_SIZE,
+            @TypeOf(ctx.*).CIPHER_FN,
+            ctx,
+        );
     }
 
-pub fn gcm_128_incr(ctr: *[Gcm128Ctx.BLOCK_SIZE]u8) void {
+    // Finally, if there's still plaintext left, update the keystream and encrypt the rest of it.
+    if (bytes_processed < plaintext.len) {
+        gcm_128_update_keystream(
+            @TypeOf(ctx.*).KEY_SIZE,
+            @TypeOf(ctx.*).CIPHER_FN,
+            ctx,
+        );
+        gcm_128_crypt_xor(
+            @TypeOf(ctx.*).KEY_SIZE,
+            @TypeOf(ctx.*).CIPHER_FN,
+            ctx,
+            plaintext[bytes_processed..],
+            ciphertext[bytes_processed..],
+            false,
+        );
+        bytes_processed += plaintext.len - bytes_processed;
+    }
+}
+
+fn gcm_128_crypt_xor(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
+    input_slice: []const u8,
+    output_slice: []u8,
+    decrypt: bool,
+) void {
+    const block_offset = ctx.ciphertext_length % GCM_128_BLOCK_SIZE;
+
+    if (input_slice.len != output_slice.len or
+        block_offset + input_slice.len > GCM_128_BLOCK_SIZE)
+        @panic("gcm_128_crypt_xor contract violated!");
+
+    const len = input_slice.len;
+    for (0..len, block_offset..block_offset + len) |ct_i, ks_i| {
+        ctx.ciphertext_buffer[ks_i] = if (decrypt)
+            input_slice[ct_i]
+        else
+            input_slice[ct_i] ^ ctx.keystream[ks_i];
+
+        output_slice[ct_i] = ctx.ciphertext_buffer[ks_i];
+    }
+    ctx.ciphertext_length += len;
+}
+
+fn gcm_128_update_keystream(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
+) void {
+    gcm_128_incr(&ctx.counter);
+    cipher_encrypt_fn(&ctx.key, &ctx.counter, &ctx.keystream);
+}
+
+fn gcm_128_authenticate_ciphertext_block(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
+) void {
+    xor(GCM_128_BLOCK_SIZE, &ctx.ghash_x, &ctx.ciphertext_buffer, &ctx.ghash_x);
+    gcm_128_mult(&ctx.ghash_x, &ctx.h, &ctx.ghash_x);
+}
+
+pub fn gcm_128_encrypt_final(
+    comptime cipher_key_size: usize,
+    cipher_encrypt_fn: gcm_128_cipher_fn_t(cipher_key_size),
+    ctx: *Gcm128Ctx(cipher_key_size, cipher_encrypt_fn),
+    tag: []u8,
+) !void {
+    if (tag.len > @TypeOf(ctx.*).TAG_MAX_BYTES)
+        return CryptoError.InvalidTagLength;
+
+    // The last ciphertext block is 0-padded and authenticated.
+    const ct_residue_bytes = ctx.ciphertext_length % GCM_128_BLOCK_SIZE;
+    @memset(ctx.ciphertext_buffer[ct_residue_bytes..], 0);
+    gcm_128_authenticate_ciphertext_block(
+        @TypeOf(ctx.*).KEY_SIZE,
+        @TypeOf(ctx.*).CIPHER_FN,
+        ctx,
+    );
+
+    // Lastly, authenticate the lengths of the AAD and the ciphertext.
+    std.mem.writeInt(u64, ctx.ciphertext_buffer[0..8], ctx.aad_length, .big);
+    std.mem.writeInt(u64, ctx.ciphertext_buffer[8..], ctx.ciphertext_length, .big);
+    gcm_128_authenticate_ciphertext_block(
+        @TypeOf(ctx.*).KEY_SIZE,
+        @TypeOf(ctx.*).CIPHER_FN,
+        ctx,
+    );
+
+    // The authentication tag is the [tag.len] leftmost bytes of the final `X` XORed with `H`.
+    xor(GCM_128_BLOCK_SIZE, &ctx.ghash_x, &ctx.h, &ctx.ghash_x);
+    @memcpy(tag[0..], ctx.ghash_x[0..tag.len]);
+}
+
+pub fn gcm_128_incr(ctr: *[GCM_128_BLOCK_SIZE]u8) void {
     const val32 = std.mem.readInt(u32, ctr[ctr.len - 4 .. ctr.len], .big);
     std.mem.writeInt(u32, ctr[ctr.len - 4 .. ctr.len], val32 +% 1, .big);
 }
 
 pub fn gcm_128_ghash_padded_chunk(
-    iv: *const [Gcm128Ctx.BLOCK_SIZE]u8,
+    iv: *const [GCM_128_BLOCK_SIZE]u8,
-    h: *const [Gcm128Ctx.BLOCK_SIZE]u8,
+    h: *const [GCM_128_BLOCK_SIZE]u8,
     chunk: []const u8,
-    out: *[Gcm128Ctx.BLOCK_SIZE]u8,
+    out: *[GCM_128_BLOCK_SIZE]u8,
 ) void {
-    const bs = Gcm128Ctx.BLOCK_SIZE;
+    const BS = GCM_128_BLOCK_SIZE;
 
-    const m = chunk.len / bs;
+    const m = chunk.len / BS;
     // Note: This definition of `v` is different from the one in the standard,
     // it is the number of residue *bytes* in the last block, not bits.
-    const v = chunk.len % bs;
+    const v = chunk.len % BS;
 
-    var x_i: [Gcm128Ctx.BLOCK_SIZE]u8 = *iv;
+    var x_i: [GCM_128_BLOCK_SIZE]u8 = iv.*;
     var i: usize = 0;
 
     while (i < m) : (i += 1) {
-        xor(bs, x_i[0..], chunk[i * bs .. (i + 1) * bs], &x_i);
+        xor(BS, x_i[0..], @ptrCast(chunk[i * BS .. (i + 1) * BS]), &x_i);
         gcm_128_mult(&x_i, h, &x_i);
     }
 
-    var padded: [Gcm128Ctx.BLOCK_SIZE]u8 = undefined;
+    var padded: [GCM_128_BLOCK_SIZE]u8 = undefined;
-    @memcpy(padded[0..v], chunk[i * bs ..]);
+    @memcpy(padded[0..v], chunk[i * BS ..]);
     @memset(padded[v..], 0x00);
 
-    xor(bs, x_i[0..], padded[0..], &x_i);
+    xor(BS, x_i[0..], padded[0..], &x_i);
     gcm_128_mult(&x_i, h, out);
 }
 
 pub fn gcm_128_ghash(
-    h: *const [Gcm128Ctx.BLOCK_SIZE]u8,
+    h: *const [GCM_128_BLOCK_SIZE]u8,
     aad_chunk: []const u8,
     ciphertext_chunk: []const u8,
-    out: *[Gcm128Ctx.BLOCK_SIZE]u8,
+    out: *[GCM_128_BLOCK_SIZE]u8,
 ) void {
-    gcm_128_ghash_padded_chunk(&std.mem.zeroes([Gcm128Ctx.BLOCK_SIZE]u8), h, aad_chunk, out);
+    gcm_128_ghash_padded_chunk(&std.mem.zeroes([GCM_128_BLOCK_SIZE]u8), h, aad_chunk, out);
     gcm_128_ghash_padded_chunk(out, h, ciphertext_chunk, out);
 
-    const bs = Gcm128Ctx.BLOCK_SIZE;
+    const BS = GCM_128_BLOCK_SIZE;
 
-    var lengths: [bs]u8 = undefined;
+    var lengths: [BS]u8 = undefined;
-    std.mem.writeInt(u64, lengths[0 .. bs / 2], aad_chunk.len * 8, .big);
+    std.mem.writeInt(u64, lengths[0 .. BS / 2], aad_chunk.len * 8, .big);
-    std.mem.writeInt(u64, lengths[bs / 2 ..], ciphertext_chunk.len * 8, .big);
+    std.mem.writeInt(u64, lengths[BS / 2 ..], ciphertext_chunk.len * 8, .big);
 
-    xor(bs, lengths[0..], out[0..], out);
+    xor(BS, lengths[0..], out[0..], out);
     gcm_128_mult(out, h, out);
 }
 
@@ -155,11 +342,12 @@ pub fn gcm_128_mult(
     const gcm_128_irreducible_R: u128 = 0xe100_0000_0000_0000_0000_0000_0000_0000;
 
     var z: u128 = 0;
-    var v = std.mem.readInt(u128, a, .big);
+    var v: u128 = std.mem.readInt(u128, a, .big);
-    const y = std.mem.readInt(u128, b, .big);
+    const y: u128 = std.mem.readInt(u128, b, .big);
 
     for (0..128) |i| {
-        if ((y >> (127 - i)) & 1 == 1)
+        const bit_index = 127 - @as(u7, @intCast(i));
+        if ((y >> bit_index) & 1 == 1)
             z ^= v;
 
         if (v & 1 == 0)
@@ -175,3 +363,54 @@ fn xor(L: comptime_int, a: *const [L]u8, b: *const [L]u8, out: *[L]u8) void {
     for (0..L) |i|
         out[i] = a[i] ^ b[i];
 }
+
+inline fn bytes_from_be_int(Int: type, value: Int) [@sizeOf(Int)]u8 {
+    var res: [@sizeOf(Int)]u8 = undefined;
+    std.mem.writeInt(Int, &res, value, .big);
+    return res;
+}
+
+const aes = @import("aes.zig");
+
+// https://csrc.nist.rip/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf
+test "AES-GCM Test Case 1" {
+    const K = bytes_from_be_int(u128, 0x00000000000000000000000000000000);
+    const P = [0]u8{};
+    const IV = std.mem.zeroes([96 / 8]u8);
+    const H = bytes_from_be_int(u128, 0x66e94bd4ef8a2c3b884cfa59ca342b2e);
+    const Y0 = bytes_from_be_int(u128, 0x00000000000000000000000000000001);
+    // const E_K_Y0 = bytes_from_be_int(u128, 0x58e2fccefa7e3061367f1d57a4e7455a);
+    // const len_A_len_C = bytes_from_be_int(u128, 0x00000000000000000000000000000000);
+    // const GHASH_H_A_C = bytes_from_be_int(u128, 0x00000000000000000000000000000000);
+    const C = [0]u8{};
+    const T = bytes_from_be_int(u128, 0x58e2fccefa7e3061367f1d57a4e7455a);
+
+    var ctx = try gcm_128_new(
+        aes.Aes128Parameters.KEY_SIZE,
+        aes.aes_128_encrypt_block,
+        &K,
+        &IV,
+    );
+
+    try testing.expectEqualSlices(u8, &H, &ctx.h);
+    try testing.expectEqualSlices(u8, &Y0, &ctx.counter);
+
+    var ciphertext_buffer = [0]u8{};
+    try gcm_128_encrypt(
+        aes.Aes128Parameters.KEY_SIZE,
+        aes.aes_128_encrypt_block,
+        &ctx,
+        &P,
+        &ciphertext_buffer,
+    );
+    try testing.expectEqualSlices(u8, &C, &ciphertext_buffer);
+
+    var tag_buffer: @TypeOf(T) = undefined;
+    try gcm_128_encrypt_final(
+        aes.Aes128Parameters.KEY_SIZE,
+        aes.aes_128_encrypt_block,
+        &ctx,
+        &tag_buffer,
+    );
+    try testing.expectEqualSlices(u8, &T, &tag_buffer);
+}

src/test.zig

@@ -2,6 +2,7 @@ comptime {
     _ = .{
         @import("./primitive/blockcipher/aes.zig"),
         @import("./primitive/blockcipher/des.zig"),
+        @import("./primitive/blockcipher/mode_gcm.zig"),
         @import("./primitive/digest/sha_1.zig"),
         @import("./primitive/digest/sha_2.zig"),
         @import("./primitive/streamcipher/chacha20.zig"),