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/*
* Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "inner.h"
static inline size_t
hash_size(const br_hash_class *dig)
{
return (unsigned)(dig->desc >> BR_HASHDESC_OUT_OFF)
& BR_HASHDESC_OUT_MASK;
}
static inline size_t
block_size(const br_hash_class *dig)
{
unsigned ls;
ls = (unsigned)(dig->desc >> BR_HASHDESC_LBLEN_OFF)
& BR_HASHDESC_LBLEN_MASK;
return (size_t)1 << ls;
}
/* see bearssl.h */
size_t
br_hmac_outCT(const br_hmac_context *ctx,
const void *data, size_t len, size_t min_len, size_t max_len,
void *out)
{
/*
* Method implemented here is inspired from the descriptions on:
* https://www.imperialviolet.org/2013/02/04/luckythirteen.html
*
* Principle: we input bytes one by one. We use a MUX to push
* padding bytes instead of data bytes when appropriate. At each
* block limit, we get the current hash function state: this is
* a potential output, since we handle MD padding ourselves.
*
* be 1 for big-endian, 0 for little-endian
* po minimal MD padding length
* bs block size (always a power of 2)
* hlen hash output size
*/
const br_hash_class *dig;
br_hash_compat_context hc;
int be;
uint32_t po, bs;
uint32_t kr, km, kl, kz, u;
uint64_t count, ncount, bit_len;
unsigned char tmp1[64], tmp2[64];
size_t hlen;
/*
* Copy the current hash context.
*/
hc = ctx->dig;
/*
* Get function-specific information.
*/
dig = hc.vtable;
be = (dig->desc & BR_HASHDESC_MD_PADDING_BE) != 0;
po = 9;
if (dig->desc & BR_HASHDESC_MD_PADDING_128) {
po += 8;
}
bs = block_size(dig);
hlen = hash_size(dig);
/*
* Get current input length and compute total bit length.
*/
count = dig->state(&hc.vtable, tmp1);
bit_len = (count + (uint64_t)len) << 3;
/*
* We can input the blocks that we are sure we will use.
* This offers better performance (no MUX for these blocks)
* and also ensures that the remaining lengths fit on 32 bits.
*/
ncount = (count + (uint64_t)min_len) & ~(uint64_t)(bs - 1);
if (ncount > count) {
size_t zlen;
zlen = (size_t)(ncount - count);
dig->update(&hc.vtable, data, zlen);
data = (const unsigned char *)data + zlen;
len -= zlen;
max_len -= zlen;
count = ncount;
}
/*
* At that point:
* -- 'count' contains the number of bytes already processed
* (in total).
* -- We must input 'len' bytes. 'min_len' is unimportant: we
* used it to know how many full blocks we could process
* directly. Now only len and max_len matter.
*
* We compute kr, kl, kz and km.
* kr number of input bytes already in the current block
* km index of the first byte after the end of the last padding
* block, if length is max_len
* kz index of the last byte of the actual last padding block
* kl index of the start of the encoded length
*
* km, kz and kl are counted from the current offset in the
* input data.
*/
kr = (uint32_t)count & (bs - 1);
kz = ((kr + (uint32_t)len + po + bs - 1) & ~(bs - 1)) - 1 - kr;
kl = kz - 7;
km = ((kr + (uint32_t)max_len + po + bs - 1) & ~(bs - 1)) - kr;
/*
* We must now process km bytes. For index u from 0 to km-1:
* d is from data[] if u < max_len, 0x00 otherwise
* e is an encoded length byte or 0x00, depending on u
* The tests for d and e need not be constant-time, since
* they relate only to u and max_len, not to the actual length.
*
* Actual input length is then:
* d if u < len
* 0x80 if u == len
* 0x00 if u > len and u < kl
* e if u >= kl
*
* Hash state is obtained whenever we reach a full block. This
* is the result we want if and only if u == kz.
*/
memset(tmp2, 0, sizeof tmp2);
for (u = 0; u < km; u ++) {
uint32_t v;
uint32_t d, e, x0, x1;
unsigned char x[1];
d = (u < max_len) ? ((const unsigned char *)data)[u] : 0x00;
v = (kr + u) & (bs - 1);
if (v >= (bs - 8)) {
unsigned j;
j = (v - (bs - 8)) << 3;
if (be) {
e = (uint32_t)(bit_len >> (56 - j));
} else {
e = (uint32_t)(bit_len >> j);
}
e &= 0xFF;
} else {
e = 0x00;
}
x0 = MUX(EQ(u, (uint32_t)len), 0x80, d);
x1 = MUX(LT(u, kl), 0x00, e);
x[0] = MUX(LE(u, (uint32_t)len), x0, x1);
dig->update(&hc.vtable, x, 1);
if (v == (bs - 1)) {
dig->state(&hc.vtable, tmp1);
CCOPY(EQ(u, kz), tmp2, tmp1, hlen);
}
}
/*
* Inner hash output is in tmp2[]; we finish processing.
*/
dig->init(&hc.vtable);
dig->set_state(&hc.vtable, ctx->kso, (uint64_t)bs);
dig->update(&hc.vtable, tmp2, hlen);
dig->out(&hc.vtable, tmp2);
memcpy(out, tmp2, ctx->out_len);
return ctx->out_len;
}
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