Problem - Kevin Tafuro

if (ol) *ol = out - start;
return 1;
}
Finalizing CBC-mode decryption is done with spc_cbc_decrypt_final( ), whose listing
follows. This function will return 1 if there are no problems or 0 if the total input
length is not a multiple of the block size or if padding is on and the padding is incorrect.
If the call is successful and padding is on, the function will write into the output
buffer anywhere from 0 to SPC_BLOCK_SZ bytes. If padding is off, a successful function
will always write SPC_BLOCK_SZ bytes into the output buffer.
As with spc_cbc_encrypt_final( ), this function will securely erase the contents of
the context object before returning.
int spc_cbc_decrypt_final(SPC_CBC_CTX *ctx, unsigned char *out, size_t *ol) {
unsigned int i;
unsigned char pad;
if (ctx->ix != SPC_BLOCK_SZ) {
if (ol) *ol = 0;
/* If there was no input, and there's no padding, then everything is OK. */
spc_memset(&(ctx->ks), 0, sizeof(SPC_KEY_SCHED));
spc_memset(ctx, 0, sizeof(SPC_CBC_CTX));
return (!ctx->ix && !ctx->pad);
}
if (!ctx->pad) {
SPC_DO_DECRYPT(&(ctx->ks), ctx->ctbuf, out);
for (i = 0; i < SPC_BLOCK_SZ / sizeof(int); i++)
((int *)out)[i] ^= ((int *)ctx->iv)[i];
if (ol) *ol = SPC_BLOCK_SZ;
spc_memset(ctx, 0, sizeof(SPC_CBC_CTX));
return 1;
}
SPC_DO_DECRYPT(&(ctx->ks), ctx->ctbuf, ctx->ctbuf);
spc_memset(&(ctx->ks), 0, sizeof(SPC_KEY_SCHED));
for (i = 0; i < SPC_BLOCK_SZ / sizeof(int); i++)
((int *)ctx->ctbuf)[i] ^= ((int *)ctx->iv)[i];
pad = ctx->ctbuf[SPC_BLOCK_SZ - 1];
if (pad > SPC_BLOCK_SZ) {
if (ol) *ol = 0;
spc_memset(ctx, 0, sizeof(SPC_CBC_CTX));
return 0;
}
for (i = 1; i < pad; i++) {
if (ctx->ctbuf[SPC_BLOCK_SZ - 1 - i] != pad) {
if (ol) *ol = 0;
spc_memset(ctx, 0, sizeof(SPC_CBC_CTX));
return 0;
}
}
for (i = 0; i < SPC_BLOCK_SZ - pad; i++)
Using a Generic CBC Mode Implementation | 185
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