On 16/05/2022 23:48, Philip Prindeville wrote:
Sorry, I shouldn't have phrased that inartfully.
There is no EVP_CIPHER_CTX_get_padding(), so how does one achieve something analogous?
From 3.0, assuming you are using provided ciphers (i.e. not engine
ones), then OSSL_CIPHER_PARAM_PADDING is a "gettable" parameter. See the
section "Gettable and Settable EVP_CIPHER_CTX parameters" on this page:
https://www.openssl.org/docs/man3.0/man3/EVP_EncryptInit_ex2.html
So you can use EVP_CIPHER_CTX_get_params() to obtain that value
(documented on the same man page as above). E.g. something like:
OSSL_PARAM params[2], *p = params;
unsigned int pad;
*p++ = OSSL_PARAM_construct_uint(OSSL_CIPHER_PARAM_PADDING,
&pad);
*p = OSSL_PARAM_construct_end();
if (!EVP_CIPHER_CTX_get_params(ctx, params)) {
/* Error */
}
Matt
On May 16, 2022, at 1:00 PM, Philip Prindeville <philipp_subx@xxxxxxxxxxxxxxxxxxxxx> wrote:
Thanks. That fixed the return value of EVP_CipherFinal().
Is there a reciprocal EVP_CIPHER_CTX_get_padding() method to find out what the default padding method is for ECB?
On May 16, 2022, at 12:41 AM, Tomas Mraz <tomas@xxxxxxxxxxx> wrote:
The EVP_CIPHER_CTX_set_padding(ctx, 0) must be called after the
EVP_CipherInit() to have an effect.
Also what is the AST_CRYPTO_AES_BLOCKSIZE value? Is it in bits (i.e,
128)?
Also res should be initialized to -1 so you do not return uninitialized
value on error.
Tomas Mraz
On Fri, 2022-05-13 at 09:49 -0600, Philip Prindeville wrote:
Hi,
I'm trying to rewrite some legacy AES_* code to use EVP_CIPHER_* so
it's forward compatible into 3.x.
My code, in a nutshell, looks like:
static int evp_cipher_aes_decrypt(const unsigned char *in, unsigned
char *out, unsigned inlen, const ast_aes_decrypt_key *key)
{
EVP_CIPHER_CTX *ctx;
int res, outlen, finallen;
unsigned char final[AST_CRYPTO_AES_BLOCKSIZE / 8];
if ((ctx = EVP_CIPHER_CTX_new()) == NULL) {
return -1;
}
EVP_CIPHER_CTX_set_padding(ctx, 0);
do {
if ((res = EVP_CipherInit(ctx, EVP_aes_128_ecb(),
key->raw, NULL, 0)) <= 0) {
break;
}
if ((res = EVP_CipherUpdate(ctx, out, &outlen, in,
inlen)) <= 0) {
break;
}
/* for ECB, this is a no-op */
if ((res = EVP_CipherFinal(ctx, final, &finallen)) <=
0) {
break;
}
res = outlen;
} while (0);
EVP_CIPHER_CTX_free(ctx);
return res;
}
It's ECB, so there's no IV. Or padding. The block size and key size
are both 128 bits.
One thing I noticed right away is that EVP_CipherUpdate() returns 1,
and sees "outlen" to zero.
And then EVP_CipherFinal() returns 0, and sets "finallen" to zero.
What's wrong with this code?
I'm trying to write "naive" code that counts on the primitives to
indicate how much resultant output is generated for the input I've
given (yes, I know that it's 1:1 in the case of ECB, but I shouldn't
have to hard-code that in case I want to use the same code with
multiple block modes).
The function is supposed to return <= 0 on error, otherwise the
number of bytes decrypted into "out" on success.
Thanks,
-Philip
--
Tomáš Mráz, OpenSSL
