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Odin/core/crypto/chacha20/chacha20.odin
T
Yawning Angel 7bed317636 core/crypto: Add chacha20 
This package implements the ChaCha20 stream cipher as specified in
RFC 8439, and the somewhat non-standard XChaCha20 variant that supports
a 192-bit nonce.

While an IETF draft for XChaCha20 standardization exists,
implementations that pre-date the draft use a 64-bit counter, instead of
the IETF-style 32-bit one.  This implementation opts for the latter as
compatibility with libsodium is more important than compatibility with
an expired IETF draft.
2021-11-17 13:59:53 +00:00

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package chacha20
import "core:crypto/util"
import "core:math/bits"
import "core:mem"
KEY_SIZE :: 32
NONCE_SIZE :: 12
XNONCE_SIZE :: 24
_MAX_CTR_IETF :: 0xffffffff
_BLOCK_SIZE :: 64
_STATE_SIZE_U32 :: 16
_ROUNDS :: 20
_SIGMA_0 : u32 : 0x61707865
_SIGMA_1 : u32 : 0x3320646e
_SIGMA_2 : u32 : 0x79622d32
_SIGMA_3 : u32 : 0x6b206574
Context :: struct {
_s: [_STATE_SIZE_U32]u32,
_buffer: [_BLOCK_SIZE]byte,
_off: int,
_is_ietf_flavor: bool,
_is_initialized: bool,
}
init :: proc (ctx: ^Context, key, nonce: []byte) {
if len(key) != KEY_SIZE {
panic("crypto/chacha20: invalid ChaCha20 key size")
}
if n_len := len(nonce); n_len != NONCE_SIZE && n_len != XNONCE_SIZE {
panic("crypto/chacha20: invalid (X)ChaCha20 nonce size")
}
k, n := key, nonce
// Derive the XChaCha20 subkey and sub-nonce via HChaCha20.
is_xchacha := len(nonce) == XNONCE_SIZE
if is_xchacha {
sub_key := ctx._buffer[:KEY_SIZE]
_hchacha20(sub_key, k, n)
k = sub_key
n = n[16:24]
}
ctx._s[0] = _SIGMA_0
ctx._s[1] = _SIGMA_1
ctx._s[2] = _SIGMA_2
ctx._s[3] = _SIGMA_3
ctx._s[4] = util.U32_LE(k[0:4])
ctx._s[5] = util.U32_LE(k[4:8])
ctx._s[6] = util.U32_LE(k[8:12])
ctx._s[7] = util.U32_LE(k[12:16])
ctx._s[8] = util.U32_LE(k[16:20])
ctx._s[9] = util.U32_LE(k[20:24])
ctx._s[10] = util.U32_LE(k[24:28])
ctx._s[11] = util.U32_LE(k[28:32])
ctx._s[12] = 0
if !is_xchacha {
ctx._s[13] = util.U32_LE(n[0:4])
ctx._s[14] = util.U32_LE(n[4:8])
ctx._s[15] = util.U32_LE(n[8:12])
} else {
ctx._s[13] = 0
ctx._s[14] = util.U32_LE(n[0:4])
ctx._s[15] = util.U32_LE(n[4:8])
// The sub-key is stored in the keystream buffer. While
// this will be overwritten in most circumstances, explicitly
// clear it out early.
mem.zero_explicit(&ctx._buffer, KEY_SIZE)
}
ctx._off = _BLOCK_SIZE
ctx._is_ietf_flavor = !is_xchacha
ctx._is_initialized = true
}
seek :: proc (ctx: ^Context, block_nr: u64) {
assert(ctx._is_initialized)
if ctx._is_ietf_flavor {
if block_nr > _MAX_CTR_IETF {
panic("crypto/chacha20: attempted to seek past maximum counter")
}
} else {
ctx._s[13] = u32(block_nr >> 32)
}
ctx._s[12] = u32(block_nr)
ctx._off = _BLOCK_SIZE
}
xor_bytes :: proc (ctx: ^Context, dst, src: []byte) {
assert(ctx._is_initialized)
// TODO: Enforcing that dst and src alias exactly or not at all
// is a good idea, though odd aliasing should be extremely uncommon.
src, dst := src, dst
if dst_len := len(dst); dst_len < len(src) {
src = src[:dst_len]
}
for remaining := len(src); remaining > 0; {
// Process multiple blocks at once
if ctx._off == _BLOCK_SIZE {
if nr_blocks := remaining / _BLOCK_SIZE; nr_blocks > 0 {
direct_bytes := nr_blocks * _BLOCK_SIZE
_do_blocks(ctx, dst, src, nr_blocks)
remaining -= direct_bytes
if remaining == 0 {
return
}
dst = dst[direct_bytes:]
src = src[direct_bytes:]
}
// If there is a partial block, generate and buffer 1 block
// worth of keystream.
_do_blocks(ctx, ctx._buffer[:], nil, 1)
ctx._off = 0
}
// Process partial blocks from the buffered keystream.
to_xor := min(_BLOCK_SIZE - ctx._off, remaining)
buffered_keystream := ctx._buffer[ctx._off:]
for i := 0; i < to_xor; i = i + 1 {
dst[i] = buffered_keystream[i] ~ src[i]
}
ctx._off += to_xor
dst = dst[to_xor:]
src = src[to_xor:]
remaining -= to_xor
}
}
keystream_bytes :: proc (ctx: ^Context, dst: []byte) {
assert(ctx._is_initialized)
dst := dst
for remaining := len(dst); remaining > 0; {
// Process multiple blocks at once
if ctx._off == _BLOCK_SIZE {
if nr_blocks := remaining / _BLOCK_SIZE; nr_blocks > 0 {
direct_bytes := nr_blocks * _BLOCK_SIZE
_do_blocks(ctx, dst, nil, nr_blocks)
remaining -= direct_bytes
if remaining == 0 {
return
}
dst = dst[direct_bytes:]
}
// If there is a partial block, generate and buffer 1 block
// worth of keystream.
_do_blocks(ctx, ctx._buffer[:], nil, 1)
ctx._off = 0
}
// Process partial blocks from the buffered keystream.
to_copy := min(_BLOCK_SIZE - ctx._off, remaining)
buffered_keystream := ctx._buffer[ctx._off:]
copy(dst[:to_copy], buffered_keystream[:to_copy])
ctx._off += to_copy
dst = dst[to_copy:]
remaining -= to_copy
}
}
reset :: proc (ctx: ^Context) {
mem.zero_explicit(&ctx._s, size_of(ctx._s))
mem.zero_explicit(&ctx._buffer, size_of(ctx._buffer))
ctx._is_initialized = false
}
_do_blocks :: proc (ctx: ^Context, dst, src: []byte, nr_blocks: int) {
// Enforce the maximum consumed keystream per nonce.
//
// While all modern "standard" definitions of ChaCha20 use
// the IETF 32-bit counter, for XChaCha20 most common
// implementations allow for a 64-bit counter.
//
// Honestly, the answer here is "use a MRAE primitive", but
// go with common practice in the case of XChaCha20.
if ctx._is_ietf_flavor {
if u64(ctx._s[12]) + u64(nr_blocks) > 0xffffffff {
panic("crypto/chacha20: maximum ChaCha20 keystream per nonce reached")
}
} else {
ctr := (u64(ctx._s[13]) << 32) | u64(ctx._s[12])
if _, carry := bits.add_u64(ctr, u64(nr_blocks), 0); carry != 0 {
panic("crypto/chacha20: maximum XChaCha20 keystream per nonce reached")
}
}
dst, src := dst, src
x := &ctx._s
for n := 0; n < nr_blocks; n = n + 1 {
x0, x1, x2, x3 := _SIGMA_0, _SIGMA_1, _SIGMA_2, _SIGMA_3
x4, x5, x6, x7, x8, x9, x10, x11, x12, x13, x14, x15 := x[4], x[5], x[6], x[7], x[8], x[9], x[10], x[11], x[12], x[13], x[14], x[15]
for i := _ROUNDS; i > 0; i = i - 2 {
// Even when forcing inlining manually inlining all of
// these is decently faster.
// quarterround(x, 0, 4, 8, 12)
x0 += x4
x12 ~= x0
x12 = util.ROTL32(x12, 16)
x8 += x12
x4 ~= x8
x4 = util.ROTL32(x4, 12)
x0 += x4
x12 ~= x0
x12 = util.ROTL32(x12, 8)
x8 += x12
x4 ~= x8
x4 = util.ROTL32(x4, 7)
// quarterround(x, 1, 5, 9, 13)
x1 += x5
x13 ~= x1
x13 = util.ROTL32(x13, 16)
x9 += x13
x5 ~= x9
x5 = util.ROTL32(x5, 12)
x1 += x5
x13 ~= x1
x13 = util.ROTL32(x13, 8)
x9 += x13
x5 ~= x9
x5 = util.ROTL32(x5, 7)
// quarterround(x, 2, 6, 10, 14)
x2 += x6
x14 ~= x2
x14 = util.ROTL32(x14, 16)
x10 += x14
x6 ~= x10
x6 = util.ROTL32(x6, 12)
x2 += x6
x14 ~= x2
x14 = util.ROTL32(x14, 8)
x10 += x14
x6 ~= x10
x6 = util.ROTL32(x6, 7)
// quarterround(x, 3, 7, 11, 15)
x3 += x7
x15 ~= x3
x15 = util.ROTL32(x15, 16)
x11 += x15
x7 ~= x11
x7 = util.ROTL32(x7, 12)
x3 += x7
x15 ~= x3
x15 = util.ROTL32(x15, 8)
x11 += x15
x7 ~= x11
x7 = util.ROTL32(x7, 7)
// quarterround(x, 0, 5, 10, 15)
x0 += x5
x15 ~= x0
x15 = util.ROTL32(x15, 16)
x10 += x15
x5 ~= x10
x5 = util.ROTL32(x5, 12)
x0 += x5
x15 ~= x0
x15 = util.ROTL32(x15, 8)
x10 += x15
x5 ~= x10
x5 = util.ROTL32(x5, 7)
// quarterround(x, 1, 6, 11, 12)
x1 += x6
x12 ~= x1
x12 = util.ROTL32(x12, 16)
x11 += x12
x6 ~= x11
x6 = util.ROTL32(x6, 12)
x1 += x6
x12 ~= x1
x12 = util.ROTL32(x12, 8)
x11 += x12
x6 ~= x11
x6 = util.ROTL32(x6, 7)
// quarterround(x, 2, 7, 8, 13)
x2 += x7
x13 ~= x2
x13 = util.ROTL32(x13, 16)
x8 += x13
x7 ~= x8
x7 = util.ROTL32(x7, 12)
x2 += x7
x13 ~= x2
x13 = util.ROTL32(x13, 8)
x8 += x13
x7 ~= x8
x7 = util.ROTL32(x7, 7)
// quarterround(x, 3, 4, 9, 14)
x3 += x4
x14 ~= x3
x14 = util.ROTL32(x14, 16)
x9 += x14
x4 ~= x9
x4 = util.ROTL32(x4, 12)
x3 += x4
x14 ~= x3
x14 = util.ROTL32(x14, 8)
x9 += x14
x4 ~= x9
x4 = util.ROTL32(x4, 7)
}
x0 += _SIGMA_0
x1 += _SIGMA_1
x2 += _SIGMA_2
x3 += _SIGMA_3
x4 += x[4]
x5 += x[5]
x6 += x[6]
x7 += x[7]
x8 += x[8]
x9 += x[9]
x10 += x[10]
x11 += x[11]
x12 += x[12]
x13 += x[13]
x14 += x[14]
x15 += x[15]
// While the "correct" answer to getting more performance out of
// this is "use vector operations", support for that is currently
// a work in progress/to be designed.
//
// Until dedicated assembly can be written leverage the fact that
// the callers of this routine ensure that src/dst are valid.
when ODIN_ARCH == "386" || ODIN_ARCH == "amd64" {
// util.PUT_U32_LE/util.U32_LE are not required on little-endian
// systems that also happen to not be strict about aligned
// memory access.
dst_p := transmute(^[16]u32)(&dst[0])
if src != nil {
src_p := transmute(^[16]u32)(&src[0])
dst_p[0] = src_p[0] ~ x0
dst_p[1] = src_p[1] ~ x1
dst_p[2] = src_p[2] ~ x2
dst_p[3] = src_p[3] ~ x3
dst_p[4] = src_p[4] ~ x4
dst_p[5] = src_p[5] ~ x5
dst_p[6] = src_p[6] ~ x6
dst_p[7] = src_p[7] ~ x7
dst_p[8] = src_p[8] ~ x8
dst_p[9] = src_p[9] ~ x9
dst_p[10] = src_p[10] ~ x10
dst_p[11] = src_p[11] ~ x11
dst_p[12] = src_p[12] ~ x12
dst_p[13] = src_p[13] ~ x13
dst_p[14] = src_p[14] ~ x14
dst_p[15] = src_p[15] ~ x15
src = src[_BLOCK_SIZE:]
} else {
dst_p[0] = x0
dst_p[1] = x1
dst_p[2] = x2
dst_p[3] = x3
dst_p[4] = x4
dst_p[5] = x5
dst_p[6] = x6
dst_p[7] = x7
dst_p[8] = x8
dst_p[9] = x9
dst_p[10] = x10
dst_p[11] = x11
dst_p[12] = x12
dst_p[13] = x13
dst_p[14] = x14
dst_p[15] = x15
}
dst = dst[_BLOCK_SIZE:]
} else {
#no_bounds_check {
if src != nil {
util.PUT_U32_LE(dst[0:4], util.U32_LE(src[0:4]) ~ x0)
util.PUT_U32_LE(dst[4:8], util.U32_LE(src[4:8]) ~ x1)
util.PUT_U32_LE(dst[8:12], util.U32_LE(src[8:12]) ~ x2)
util.PUT_U32_LE(dst[12:16], util.U32_LE(src[12:16]) ~ x3)
util.PUT_U32_LE(dst[16:20], util.U32_LE(src[16:20]) ~ x4)
util.PUT_U32_LE(dst[20:24], util.U32_LE(src[20:24]) ~ x5)
util.PUT_U32_LE(dst[24:28], util.U32_LE(src[24:28]) ~ x6)
util.PUT_U32_LE(dst[28:32], util.U32_LE(src[28:32]) ~ x7)
util.PUT_U32_LE(dst[32:36], util.U32_LE(src[32:36]) ~ x8)
util.PUT_U32_LE(dst[36:40], util.U32_LE(src[36:40]) ~ x9)
util.PUT_U32_LE(dst[40:44], util.U32_LE(src[40:44]) ~ x10)
util.PUT_U32_LE(dst[44:48], util.U32_LE(src[44:48]) ~ x11)
util.PUT_U32_LE(dst[48:52], util.U32_LE(src[48:52]) ~ x12)
util.PUT_U32_LE(dst[52:56], util.U32_LE(src[52:56]) ~ x13)
util.PUT_U32_LE(dst[56:60], util.U32_LE(src[56:60]) ~ x14)
util.PUT_U32_LE(dst[60:64], util.U32_LE(src[60:64]) ~ x15)
src = src[_BLOCK_SIZE:]
} else {
util.PUT_U32_LE(dst[0:4], x0)
util.PUT_U32_LE(dst[4:8], x1)
util.PUT_U32_LE(dst[8:12], x2)
util.PUT_U32_LE(dst[12:16], x3)
util.PUT_U32_LE(dst[16:20], x4)
util.PUT_U32_LE(dst[20:24], x5)
util.PUT_U32_LE(dst[24:28], x6)
util.PUT_U32_LE(dst[28:32], x7)
util.PUT_U32_LE(dst[32:36], x8)
util.PUT_U32_LE(dst[36:40], x9)
util.PUT_U32_LE(dst[40:44], x10)
util.PUT_U32_LE(dst[44:48], x11)
util.PUT_U32_LE(dst[48:52], x12)
util.PUT_U32_LE(dst[52:56], x13)
util.PUT_U32_LE(dst[56:60], x14)
util.PUT_U32_LE(dst[60:64], x15)
}
dst = dst[_BLOCK_SIZE:]
}
}
// Increment the counter. Overflow checking is done upon
// entry into the routine, so a 64-bit increment safely
// covers both cases.
new_ctr := ((u64(ctx._s[13]) << 32) | u64(ctx._s[12])) + 1
x[12] = u32(new_ctr)
x[13] = u32(new_ctr >> 32)
}
}
_hchacha20 :: proc (dst, key, nonce: []byte) {
x0, x1, x2, x3 := _SIGMA_0, _SIGMA_1, _SIGMA_2, _SIGMA_3
x4 := util.U32_LE(key[0:4])
x5 := util.U32_LE(key[4:8])
x6 := util.U32_LE(key[8:12])
x7 := util.U32_LE(key[12:16])
x8 := util.U32_LE(key[16:20])
x9 := util.U32_LE(key[20:24])
x10 := util.U32_LE(key[24:28])
x11 := util.U32_LE(key[28:32])
x12 := util.U32_LE(nonce[0:4])
x13 := util.U32_LE(nonce[4:8])
x14 := util.U32_LE(nonce[8:12])
x15 := util.U32_LE(nonce[12:16])
for i := _ROUNDS; i > 0; i = i - 2 {
// quarterround(x, 0, 4, 8, 12)
x0 += x4
x12 ~= x0
x12 = util.ROTL32(x12, 16)
x8 += x12
x4 ~= x8
x4 = util.ROTL32(x4, 12)
x0 += x4
x12 ~= x0
x12 = util.ROTL32(x12, 8)
x8 += x12
x4 ~= x8
x4 = util.ROTL32(x4, 7)
// quarterround(x, 1, 5, 9, 13)
x1 += x5
x13 ~= x1
x13 = util.ROTL32(x13, 16)
x9 += x13
x5 ~= x9
x5 = util.ROTL32(x5, 12)
x1 += x5
x13 ~= x1
x13 = util.ROTL32(x13, 8)
x9 += x13
x5 ~= x9
x5 = util.ROTL32(x5, 7)
// quarterround(x, 2, 6, 10, 14)
x2 += x6
x14 ~= x2
x14 = util.ROTL32(x14, 16)
x10 += x14
x6 ~= x10
x6 = util.ROTL32(x6, 12)
x2 += x6
x14 ~= x2
x14 = util.ROTL32(x14, 8)
x10 += x14
x6 ~= x10
x6 = util.ROTL32(x6, 7)
// quarterround(x, 3, 7, 11, 15)
x3 += x7
x15 ~= x3
x15 = util.ROTL32(x15, 16)
x11 += x15
x7 ~= x11
x7 = util.ROTL32(x7, 12)
x3 += x7
x15 ~= x3
x15 = util.ROTL32(x15, 8)
x11 += x15
x7 ~= x11
x7 = util.ROTL32(x7, 7)
// quarterround(x, 0, 5, 10, 15)
x0 += x5
x15 ~= x0
x15 = util.ROTL32(x15, 16)
x10 += x15
x5 ~= x10
x5 = util.ROTL32(x5, 12)
x0 += x5
x15 ~= x0
x15 = util.ROTL32(x15, 8)
x10 += x15
x5 ~= x10
x5 = util.ROTL32(x5, 7)
// quarterround(x, 1, 6, 11, 12)
x1 += x6
x12 ~= x1
x12 = util.ROTL32(x12, 16)
x11 += x12
x6 ~= x11
x6 = util.ROTL32(x6, 12)
x1 += x6
x12 ~= x1
x12 = util.ROTL32(x12, 8)
x11 += x12
x6 ~= x11
x6 = util.ROTL32(x6, 7)
// quarterround(x, 2, 7, 8, 13)
x2 += x7
x13 ~= x2
x13 = util.ROTL32(x13, 16)
x8 += x13
x7 ~= x8
x7 = util.ROTL32(x7, 12)
x2 += x7
x13 ~= x2
x13 = util.ROTL32(x13, 8)
x8 += x13
x7 ~= x8
x7 = util.ROTL32(x7, 7)
// quarterround(x, 3, 4, 9, 14)
x3 += x4
x14 ~= x3
x14 = util.ROTL32(x14, 16)
x9 += x14
x4 ~= x9
x4 = util.ROTL32(x4, 12)
x3 += x4
x14 ~= x3
x14 = util.ROTL32(x14, 8)
x9 += x14
x4 ~= x9
x4 = util.ROTL32(x4, 7)
}
util.PUT_U32_LE(dst[0:4], x0)
util.PUT_U32_LE(dst[4:8], x1)
util.PUT_U32_LE(dst[8:12], x2)
util.PUT_U32_LE(dst[12:16], x3)
util.PUT_U32_LE(dst[16:20], x12)
util.PUT_U32_LE(dst[20:24], x13)
util.PUT_U32_LE(dst[24:28], x14)
util.PUT_U32_LE(dst[28:32], x15)
}
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