Dr. Stephen Henson wrote:
>On Fri, Sep 10, 2004, Dr. Stephen Henson wrote:
>
>
>
>>On Fri, Sep 10, 2004, Steve Hay wrote:
>>
>>
>>
>>>As an alternative to my luckless attempts at using
>>>EVP_CIPHER_param_to_asn1() + PKCS5_v2_PBE_keyivgen(), I thought I would
>>>try PKCS5_pbe2_set() + EVP_PBE_CipherInit(), but I've run into the
>>>problem that I thought I would have: PKCS5_pbe2_set() randomly
>>>generates its own IV, so that trying to decrypt previously encrypted
>>>data doesn't work. (Or at least, I think that's what the problem is.)
>>>
>>>I thought that calling
>>>
>>> EVP_CipherInit_ex(&ctx, cipher, NULL, NULL, iv, crypt_mode);
>>>
>>>after the EVP_PBE_CipherInit() call would replace the iv set by
>>>PKCS5_pbe2_set() with my own one, but it seems to make no difference, as
>>>the attached sample program demonstrates.
>>>
>>>
>>>
>>Currently you can't set the IV yourself in PKCS5_pbe2_set(). If you however
>>just want to save and restore the random IV (along with the parameters used
>>for the key) you can use the {i2d,d2i}_ASN1_TYPE() functions to save and
>>restore this to and from a memory buffer along with the salt and key length.
>>
>>
>>
>
>Actually you'd be better just encoding and decoding the X509_ALGOR structure
>(pbe2 I believe you called it) before the data and on the decode side passing
>*that* to EVP_PBE_CipherInit().
>
OK, I tried that and it works very well.
However, as the attached program shows, it now turns out that this has
all been a waste of time. If you recall what my original problem was
(namely, EVP_BytesToKey() only supports default key length -- see
http://www.mail-archive.com/[EMAIL PROTECTED]/msg37111.html),
the main reason for switching to EVP_PBE_CipherInit() was that
PKCS5_v2_PBE_keyivgen(), which is called by EVP_PBE_CipherInit(),
supposedly works with non-default key lengths. But now that I've
finally got it working I find that it doesn't support non-default key
lengths after all.
Walking through the attached program in a debugger, I see that my
EVP_CIPHER_CTX_set_key_length() call correctly sets the key length to 24
(whereas BF default is 16), but then PKCS5_v2_PBE_keyivgen() does this:
/* Fixup cipher based on AlgorithmIdentifier */
EVP_CipherInit_ex(ctx, cipher, NULL, NULL, NULL, en_de);
(crypto/evp/p5_crpt2.c line 185-6 in openssl-0.9.7d), which has the
effect of resetting the key length in the ctx to the cipher's default,
namely 16 here!
So now I'm back to square one: How do I do PKCS#5 key derivation using a
non-default key length?
- Steve
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#include <stdio.h>
#include <openssl/evp.h>
#include <openssl/rand.h>
#include <openssl/x509.h>
int main(int argc, char **argv) {
FILE *in, *out;
if (argc != 4) {
printf("Usage: %s infile outfile cryptmode\n", argv[0]);
return 2;
}
if ((in = fopen(argv[1], "rb")) == NULL) {
printf("Error reading input\n");
return 3;
}
if ((out = fopen(argv[2], "wb")) == NULL) {
printf("Error writing output\n");
return 4;
}
if (do_crypt(in, out, atoi(argv[3])) == 0) {
printf("Error running do_crypt()\n");
return 5;
}
return 0;
}
#define KEYLEN 24
const unsigned char pswd[] = "0123456789ABCDEFGHIJKLMN";
int do_crypt(FILE *in, FILE *out, int crypt_mode) {
unsigned char inbuf[BUFSIZ], outbuf[BUFSIZ + EVP_MAX_BLOCK_LENGTH];
int inlen, outlen;
unsigned char salt[PKCS5_SALT_LEN];
const EVP_CIPHER *cipher = EVP_bf_cbc();
X509_ALGOR *pbe2;
EVP_CIPHER_CTX ctx;
int len;
unsigned char *buf, *p;
char lenstr[10];
if (crypt_mode) {
if (!RAND_bytes(salt, PKCS5_SALT_LEN))
return 0;
pbe2 = PKCS5_pbe2_set(cipher, PKCS5_DEFAULT_ITER, salt, PKCS5_SALT_LEN);
len = i2d_X509_ALGOR(pbe2, NULL);
buf = OPENSSL_malloc(len);
p = buf;
i2d_X509_ALGOR(pbe2, &p);
itoa(len, lenstr, 10);
fwrite(lenstr, 1, strlen(lenstr) + 1, out); // Include '\0' in output
fwrite(buf, 1, len, out);
OPENSSL_free(buf);
}
else {
fscanf(in, "%10[^\0]%*[\0]", lenstr);
len = atoi(lenstr);
buf = OPENSSL_malloc(len);
fread(buf, 1, len, in);
p = buf;
pbe2 = NULL;
d2i_X509_ALGOR(&pbe2, &p, len);
OPENSSL_free(buf);
}
EVP_add_cipher(cipher);
PKCS5_PBE_add();
EVP_CIPHER_CTX_init(&ctx);
EVP_CipherInit_ex(&ctx, cipher, NULL, NULL, NULL, crypt_mode);
EVP_CIPHER_CTX_set_key_length(&ctx, KEYLEN);
if (!EVP_PBE_CipherInit(pbe2->algorithm, pswd, KEYLEN, pbe2->parameter,
&ctx, crypt_mode))
return 0;
printf("Key length: %d\n", EVP_CIPHER_CTX_key_length(&ctx));
for (;;) {
if ((inlen = fread(inbuf, 1, BUFSIZ, in)) < 0)
return 0;
else if (inlen == 0)
break;
if (!EVP_CipherUpdate(&ctx, outbuf, &outlen, inbuf, inlen))
return 0;
fwrite(outbuf, 1, outlen, out);
}
if (!EVP_CipherFinal_ex(&ctx, outbuf, &outlen))
return 0;
fwrite(outbuf, 1, outlen, out);
EVP_CIPHER_CTX_cleanup(&ctx);
EVP_cleanup();
return 1;
}
