Problem - Kevin Tafuro

if (!il--) return 1;
ctx->nonce[ctx->ix] = *out++ = *in++ ^ ctx->nonce[ctx->ix++];
ctx->ix %= SPC_BLOCK_SZ;
}
}
if (!il) return 1;
while (il >= SPC_BLOCK_SZ) {
SPC_DO_ENCRYPT(&(ctx->ks), ctx->nonce, ctx->nonce);
for (i = 0; i < SPC_BLOCK_SZ / sizeof(int); i++) {
((int *)ctx->nonce)[i] = ((int *)out)[i] = ((int *)in)[i] ^
((int *)ctx->nonce)[i];
}
il -= SPC_BLOCK_SZ;
in += SPC_BLOCK_SZ;
out += SPC_BLOCK_SZ;
}
SPC_DO_ENCRYPT(&(ctx->ks), ctx->nonce, ctx->nonce);
for (i = 0; i nonce[ctx->ix] = *out++ = *in++ ^ ctx->nonce[ctx->ix++];
return 1;
}
Decryption has a similar API, but a different implementation:
int spc_cfb_decrypt_update(SPC_CFB_CTX *ctx, unsigned char *in, size_t il,
unsigned char *out) {
int i, x;
char c;
if (ctx->ix) {
while (ctx->ix) {
if (!il--) return 1;
c = *in;
*out++ = *in++ ^ ctx->nonce[ctx->ix];
ctx->nonce[ctx->ix++] = c;
ctx->ix %= SPC_BLOCK_SZ;
}
}
if (!il) return 1;
while (il >= SPC_BLOCK_SZ) {
SPC_DO_ENCRYPT(&(ctx->ks), ctx->nonce, ctx->nonce);
for (i = 0; i < SPC_BLOCK_SZ / sizeof(int); i++) {
x = ((int *)in)[i];
((int *)out)[i] = x ^ ((int *)ctx->nonce)[i];
((int *)ctx->nonce)[i] = x;
}
il -= SPC_BLOCK_SZ;
in += SPC_BLOCK_SZ;
out += SPC_BLOCK_SZ;
}
SPC_DO_ENCRYPT(&(ctx->ks), ctx->nonce, ctx->nonce);
for (i = 0; i < il; i++) {
c = *in;
Using a Generic CFB Mode Implementation | 191
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