Decrypt char* using PKCS7_decrypt() in openssl

Question

I want to encrypt and decrypt using PKCS7_encrypt() and PKCS7_decrypt() functions in openSSL. I have used the example in openSSL Demo. What I want to do is to encrypt a message in the format of char* and decrypt using that char*. I don't want to read and write into file. Here is the code to encrypt, which perfectly works and has no problem:

in = BIO_new_file("encr.txt", "r");
if (!in)
    return 0;

/* encrypt content */
p7 = PKCS7_encrypt(recips, in, EVP_des_ede3_cbc(), flags);
if (!p7)
    return 0;

char* chEnc = new char[1000];

BIO* memorybio = BIO_new(BIO_s_mem());
BIO* base64bio = BIO_new(BIO_f_base64());
BIO* outbio = BIO_push(base64bio, memorybio);

/* Copy PKCS#7 */
long ll = i2d_PKCS7_bio(outbio, p7);
BIO_flush(outbio);
BIO_set_flags(memorybio, BIO_FLAGS_MEM_RDONLY);
BIO_get_mem_data(memorybio, &chEnc);
cout << chEnc << "\n";

Now, when I want to do the reverse and decrypt the char* chEnc, I did as below:

BIO *in = NULL, *out = NULL, *tbio = NULL;
X509 *rcert = NULL;
EVP_PKEY *rkey = NULL;
PKCS7 *p7 = NULL;
int ret = 1;

OpenSSL_add_all_algorithms();
ERR_load_crypto_strings();

/* Read in recipient certificate and private key */
tbio = BIO_new_file("signer.pem", "r");

if (!tbio)
    return 0;

rcert = PEM_read_bio_X509(tbio, NULL, 0, NULL);
BIO_reset(tbio);
rkey = PEM_read_bio_PrivateKey(tbio, NULL, 0, NULL);
if (!rcert || !rkey)
    return 0;

BIO* memorybio = BIO_new(BIO_s_mem());
int iLength = BIO_puts(memorybio, chEnc);

BIO* base64bio = BIO_new(BIO_f_base64());
BIO* inbio = BIO_push(base64bio, memorybio);

/* Copy PKCS#7 */
BIO_flush(inbio);
BIO_set_flags(inbio, BIO_FLAGS_MEM_RDONLY);
p7 = d2i_PKCS7_bio(inbio, &p7);
if (!PKCS7_decrypt(p7, rkey, rcert, out, 0))
    return 0;

ret = 0;

if (ret) {
    fprintf(stderr, "Error Signing Data\n");
    ERR_print_errors_fp(stderr);
}

if (p7)
    PKCS7_free(p7);
if (rcert)
    X509_free(rcert);
if (rkey)
    EVP_PKEY_free(rkey);

if (in)
    BIO_free(in);
if (out)
    BIO_free(out);
if (tbio)
    BIO_free(tbio);

return ret;

The problem is that the PKCS7_decrypt does not work and it does not decrypt into out variable. After the line if (!PKCS7_decrypt(p7, rkey, rcert, out, 0)) return 0; , it returns from the function. Is the procedure to decrypt correct? Shall I use other APIs of openSSL to convert or something?

Looking forward to your suggestions and comments.

Thanks

score 1 · Answer 1 · edited Nov 25 '14 at 20:05

1

PKCS7_decrypt(p7, rkey, rcert, out, 0) is failing because the BIO "out" that you are passing to the routine is a null pointer.

If you do not want to write the output into a file, try passing a memory BIO:

BIO *out = BIO_new(BIO_s_mem());

Then you can access the decrypted data directly from out, and once you are done with it you can destroy it.

edited Nov 25 '14 at 20:05

lennon310

12,503
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answered Nov 25 '14 at 19:49

Luis Enrique

11
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score 0 · Answer 2 · answered Dec 11 '12 at 21:56

0

Are you on your recipient list? Because you need to be the recipient to decrypt the message. Make sure you use the correct key and certificates.

answered Dec 11 '12 at 21:56

foo

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Decrypt char* using PKCS7_decrypt() in openssl

2 Answers2