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feat: add cbcDecrypt and cbcEncrypt modes #19321

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feat: add cbcDecrypt and cbcEncrypt modes #19321

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52 changes: 52 additions & 0 deletions lib/std/crypto/aes.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -52,6 +52,58 @@ test "ctr" {
try testing.expectEqualSlices(u8, exp_out[0..], out[0..]);
}

test "cbc encrypt" {
// NIST SP 800-38A pp 27-29
const cbc = @import("modes.zig").cbcEncrypt;

const key = [_]u8{ 0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6, 0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c };
const iv = [_]u8{ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f };
const in = [_]u8{
0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c, 0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
0x30, 0xc8, 0x1c, 0x46, 0xa3, 0x5c, 0xe4, 0x11, 0xe5, 0xfb, 0xc1, 0x19, 0x1a, 0x0a, 0x52, 0xef,
0xf6, 0x9f, 0x24, 0x45, 0xdf, 0x4f, 0x9b, 0x17, 0xad, 0x2b, 0x41, 0x7b, 0xe6, 0x6c, 0x37, 0x10,
};
const exp_out = [_]u8{
0x76, 0x49, 0xab, 0xac, 0x81, 0x19, 0xb2, 0x46, 0xce, 0xe9, 0x8e, 0x9b, 0x12, 0xe9, 0x19, 0x7d,
0x50, 0x86, 0xcb, 0x9b, 0x50, 0x72, 0x19, 0xee, 0x95, 0xdb, 0x11, 0x3a, 0x91, 0x76, 0x78, 0xb2,
0x73, 0xbe, 0xd6, 0xb8, 0xe3, 0xc1, 0x74, 0x3b, 0x71, 0x16, 0xe6, 0x9e, 0x22, 0x22, 0x95, 0x16,
0x3f, 0xf1, 0xca, 0xa1, 0x68, 0x1f, 0xac, 0x09, 0x12, 0x0e, 0xca, 0x30, 0x75, 0x86, 0xe1, 0xa7,
};

var out: [exp_out.len]u8 = undefined;

const ctx = Aes128.initEnc(key);
cbc(AesEncryptCtx(Aes128), ctx, out[0..], in[0..], iv);
try testing.expectEqualSlices(u8, exp_out[0..], out[0..]);
}

test "cbc decrypt" {
// NIST SP 800-38A pp 27-29
const cbc = @import("modes.zig").cbcDecrypt;

const key = [_]u8{ 0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6, 0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c };
const iv = [_]u8{ 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f };
const in = [_]u8{
0x76, 0x49, 0xab, 0xac, 0x81, 0x19, 0xb2, 0x46, 0xce, 0xe9, 0x8e, 0x9b, 0x12, 0xe9, 0x19, 0x7d,
0x50, 0x86, 0xcb, 0x9b, 0x50, 0x72, 0x19, 0xee, 0x95, 0xdb, 0x11, 0x3a, 0x91, 0x76, 0x78, 0xb2,
0x73, 0xbe, 0xd6, 0xb8, 0xe3, 0xc1, 0x74, 0x3b, 0x71, 0x16, 0xe6, 0x9e, 0x22, 0x22, 0x95, 0x16,
0x3f, 0xf1, 0xca, 0xa1, 0x68, 0x1f, 0xac, 0x09, 0x12, 0x0e, 0xca, 0x30, 0x75, 0x86, 0xe1, 0xa7,
};
const exp_out = [_]u8{
0x6b, 0xc1, 0xbe, 0xe2, 0x2e, 0x40, 0x9f, 0x96, 0xe9, 0x3d, 0x7e, 0x11, 0x73, 0x93, 0x17, 0x2a,
0xae, 0x2d, 0x8a, 0x57, 0x1e, 0x03, 0xac, 0x9c, 0x9e, 0xb7, 0x6f, 0xac, 0x45, 0xaf, 0x8e, 0x51,
0x30, 0xc8, 0x1c, 0x46, 0xa3, 0x5c, 0xe4, 0x11, 0xe5, 0xfb, 0xc1, 0x19, 0x1a, 0x0a, 0x52, 0xef,
0xf6, 0x9f, 0x24, 0x45, 0xdf, 0x4f, 0x9b, 0x17, 0xad, 0x2b, 0x41, 0x7b, 0xe6, 0x6c, 0x37, 0x10,
};

var out: [exp_out.len]u8 = undefined;

const ctx = Aes128.initDec(key);
cbc(AesDecryptCtx(Aes128), ctx, out[0..], in[0..], iv);
try testing.expectEqualSlices(u8, exp_out[0..], out[0..]);
}

test "encrypt" {
// Appendix B
{
Expand Down
68 changes: 68 additions & 0 deletions lib/std/crypto/modes.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -45,3 +45,71 @@ pub fn ctr(comptime BlockCipher: anytype, block_cipher: BlockCipher, dst: []u8,
@memcpy(dst[i..][0..pad_slice.len], pad_slice);
}
}

/// Cipher block chaining mode (decryption).
///
/// First decrypts with cipher, then XORs with previous block (or initialization vector).
pub fn cbcDecrypt(BlockCipher: anytype, block_cipher: BlockCipher, dst: []u8, src: []const u8, iv: [BlockCipher.block_length]u8) void {
// TODO: Add support for parallel decryption
std.debug.assert(dst.len >= src.len);
const block_length = BlockCipher.block_length;
var i: usize = 0;
var previous_block: [block_length]u8 = iv;
while (i + block_length < src.len) : (i += block_length) {
var block: [block_length]u8 = undefined;
// xor block with last block or initialization vector
block_cipher.decrypt(&block, src[i..][0..block_length]);
for (block[0..], previous_block[0..]) |*byte, prev| {
byte.* ^= prev;
}
// update last block value
@memcpy(dst[i..][0..block_length], &block);
@memcpy(&previous_block, src[i..][0..block_length]);
}
// account for unaligned final block
if (i < src.len) {
var pad = [_]u8{0} ** block_length;
const src_slice = src[i..];
@memcpy(pad[0..src_slice.len], src_slice);
block_cipher.decrypt(&pad, &pad);
for (pad[0..], previous_block[0..]) |*byte, prev| {
byte.* ^= prev;
}
const pad_slice = pad[0 .. src.len - i];
@memcpy(dst[i..][0..pad_slice.len], pad_slice);
}
}

/// Cipher block chaining mode (encryption).
///
/// First XORs each block with the previous block (or initialization vector) and then
/// encrypts the block with cipher.
pub fn cbcEncrypt(BlockCipher: anytype, block_cipher: BlockCipher, dst: []u8, src: []const u8, iv: [BlockCipher.block_length]u8) void {
std.debug.assert(dst.len >= src.len);
const block_length = BlockCipher.block_length;
var i: usize = 0;
var previous_block: [block_length]u8 = iv;
while (i + block_length < src.len) : (i += block_length) {
var block: [block_length]u8 = undefined;
// xor block with last block or initialization vector
for (block[0..], src[i..][0..block_length], previous_block[0..]) |*byte, cur, prev| {
byte.* = cur ^ prev;
}
block_cipher.encrypt(&block, &block);
// update last block value
@memcpy(dst[i..][0..block_length], block[0..block_length]);
@memcpy(&previous_block, &block);
}
// account for unaligned final block
if (i < src.len) {
var pad = [_]u8{0} ** block_length;
const src_slice = src[i..];
@memcpy(pad[0..src_slice.len], src_slice);
for (pad[0..], previous_block[0..]) |*byte, prev| {
byte.* ^= prev;
}
block_cipher.encrypt(&pad, &pad);
const pad_slice = pad[0 .. src.len - i];
@memcpy(dst[i..][0..pad_slice.len], pad_slice);
}
}