boringssl/crypto/fipsmodule/modes/ofb.c

/* ====================================================================
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#include <assert.h>
#include <string.h>

#include "internal.h"


static_assert(16 % sizeof(size_t) == 0, "block cannot be divided into size_t");

void CRYPTO_ofb128_encrypt(const uint8_t *in, uint8_t *out, size_t len,
                           const AES_KEY *key, uint8_t ivec[16], unsigned *num,
                           block128_f block) {
  assert(key != NULL && ivec != NULL && num != NULL);
  assert(len == 0 || (in != NULL && out != NULL));

  unsigned n = *num;

  while (n && len) {
    *(out++) = *(in++) ^ ivec[n];
    --len;
    n = (n + 1) % 16;
  }

  while (len >= 16) {
    (*block)(ivec, ivec, key);
    for (; n < 16; n += sizeof(size_t)) {
      size_t a, b;
      OPENSSL_memcpy(&a, in + n, sizeof(size_t));
      OPENSSL_memcpy(&b, ivec + n, sizeof(size_t));

      const size_t c = a ^ b;
      OPENSSL_memcpy(out + n, &c, sizeof(size_t));
    }
    len -= 16;
    out += 16;
    in += 16;
    n = 0;
  }
  if (len) {
    (*block)(ivec, ivec, key);
    while (len--) {
      out[n] = in[n] ^ ivec[n];
      ++n;
    }
  }
  *num = n;
}