int PKCS7_decrypt(PKCS7 *p7, EVP_PKEY *pkey, X509 *cert, BIO *data, int flags);
PKCS7_decrypt() extracts and decrypts the content from a PKCS#7 envelopedData structure. pkey is the private key of the recipient, cert is the recipients certificate, data is a BIO to write the content to and flags is an optional set of flags.
OpenSSL_add_all_algorithms() (or equivalent) should be called before using this function or errors about unknown algorithms will occur.
Although the recipients certificate is not needed to decrypt the data it is needed to locate the appropriate (of possible several) recipients in the PKCS#7 structure.
The following flags can be passed in the flags parameter.
If the PKCS7_TEXT flag is set MIME headers for type text/plain are deleted from the content. If the content is not of type text/plain then an error is returned.
PKCS7_decrypt() returns either 1 for success or 0 for failure. The error can be obtained from ERR_get_error(3)
PKCS7_decrypt() must be passed the correct recipient key and certificate. It would be better if it could look up the correct key and certificate from a database.
The lack of single pass processing and need to hold all data in memory as mentioned in PKCS7_sign() also applies to PKCS7_verify().