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cipher/chacha20: buffer the full input block 

The final implementation is simpler, at the cost of doing work in
chacha20_x_final.
This commit is contained in:
Lucas Gabriel Vuotto 2024-06-07 00:29:17 +00:00
parent 5bd46fffa6
commit e5215ac18e
2 changed files with 55 additions and 54 deletions
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106
cipher_chacha20.c
View File

@ -42,7 +42,7 @@ chacha20_x_init_from(void *arg, const uint8_t *key, size_t keylen,
ctx->c = counter;
for (i = 0; i < CHACHA20_NONCE_WORDS; i++)
ctx->n[i] = load32le(&iv[i * 4]);
ctx->blen = 0;
ctx->mlen = 0;
return 1;
}
@ -59,50 +59,42 @@ chacha20_x_update(void *arg, uint8_t *out, size_t *outlen, const uint8_t *in,
size_t inlen)
{
struct chacha20_ctx *ctx = arg;
size_t i, blocks;
uint32_t h;
uint8_t s[4];
size_t i, blocks, off, pad;
*outlen = 0;
if (inlen > SIZE_MAX - (CHACHA20_CHUNK - 1) - ctx->blen)
if (inlen > SIZE_MAX - (CHACHA20_CHUNK - 1) - ctx->mlen)
return 0;
blocks = inlen + ctx->blen + CHACHA20_CHUNK - 1;
if (blocks / CHACHA20_CHUNK + ctx->c > CHACHA20_CTRMAX)
blocks = (inlen + ctx->mlen + CHACHA20_CHUNK - 1) / CHACHA20_CHUNK;
if (blocks + ctx->c > CHACHA20_CTRMAX)
return 0;
if (out == NULL) {
*outlen = inlen;
*outlen = (ctx->mlen + inlen) / CHACHA20_CHUNK * CHACHA20_CHUNK;
if (out == NULL)
return 1;
for (i = 0; i + ctx->mlen < CHACHA20_CHUNK && i < inlen; i++)
ctx->m[i + ctx->mlen] = in[i];
ctx->mlen += i;
in += i;
inlen -= i;
if (ctx->mlen == CHACHA20_CHUNK) {
chacha20_block(ctx);
ctx->c++;
for (i = 0; i < CHACHA20_CHUNK_WORDS; i++) {
h = load32le(&ctx->m[i * 4]);
h ^= ctx->s[i];
store32le(&out[i * 4], h);
}
out += CHACHA20_CHUNK;
ctx->mlen = 0;
}
*outlen = inlen;
if (inlen == 0)
return 1;
if (ctx->blen == 0)
goto fullblock;
off = ctx->blen % 4;
if (off != 0) {
store32le(s, ctx->s[ctx->blen / 4]);
for (i = 0; i + off < 4 && i < inlen; i++)
out[i] = in[i] ^ s[i + off];
ctx->blen += i;
out += i;
in += i;
inlen -= i;
}
pad = inlen % 4;
for (i = 0; i + ctx->blen < CHACHA20_CHUNK && i < inlen - pad; i += 4) {
h = load32le(&in[i * 4]);
h ^= ctx->s[(i + ctx->blen) / 4];
store32le(&out[i * 4], h);
}
ctx->blen += i * 4;
out += i * 4;
in += i * 4;
inlen -= i * 4;
fullblock:
while (inlen >= CHACHA20_CHUNK) {
chacha20_block(ctx);
ctx->c++;
@ -117,23 +109,9 @@ chacha20_x_update(void *arg, uint8_t *out, size_t *outlen, const uint8_t *in,
inlen -= CHACHA20_CHUNK;
}
chacha20_block(ctx);
ctx->c++;
ctx->blen = inlen;
pad = inlen % 4;
for (i = 0; i < (inlen - pad) / 4; i++) {
h = load32le(&in[i * 4]);
h ^= ctx->s[i];
store32le(&out[i * 4], h);
}
out += i * 4;
in += i * 4;
inlen -= i * 4;
store32le(s, ctx->s[i]);
for (i = 0; i < pad; i++)
out[i] = in[i] ^ s[i];
for (i = 0; i < inlen; i++)
ctx->m[i] = in[i];
ctx->mlen = inlen;
return 1;
}
@ -142,8 +120,30 @@ int
chacha20_x_final(void *arg, uint8_t *out, size_t *outlen)
{
struct chacha20_ctx *ctx = arg;
size_t i, off;
uint32_t h;
uint8_t s[4];
*outlen = ctx->mlen;
if (out == NULL)
return 1;
if (ctx->mlen > 0)
chacha20_block(ctx);
for (i = 0; i < ctx->mlen / 4; i++) {
h = load32le(&ctx->m[i * 4]);
h ^= ctx->s[i];
store32le(&out[i * 4], h);
}
off = i * 4;
ctx->mlen -= off;
out += off;
store32le(&s[0], ctx->s[i]);
for (i = 0; i < ctx->mlen; i++)
out[i] = ctx->m[i + off] ^ s[i];
*outlen = 0;
lc_scrub(ctx, sizeof(*ctx));
return 1;

3
impl_chacha20.h
View File

@ -33,7 +33,8 @@ struct chacha20_ctx {
uint32_t k[CHACHA20_KEY_WORDS];
uint32_t c;
uint32_t n[CHACHA20_NONCE_WORDS];
size_t blen;
size_t mlen;
uint8_t m[CHACHA20_CHUNK];
};