NAME

       EVP_PKEY_ctrl, EVP_PKEY_ctrl_str - algorithm specific control operations

SYNOPSIS

        #include <openssl/evp.h>

        int EVP_PKEY_CTX_ctrl(EVP_PKEY_CTX *ctx, int keytype, int optype,
                                       int cmd, int p1, void *p2);
        int EVP_PKEY_CTX_ctrl_str(EVP_PKEY_CTX *ctx, const char *type,
                                                       const char *value);

        int EVP_PKEY_get_default_digest_nid(EVP_PKEY *pkey, int *pnid);

        #include <openssl/rsa.h>

        int EVP_PKEY_CTX_set_signature_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);

        int EVP_PKEY_CTX_set_rsa_padding(EVP_PKEY_CTX *ctx, int pad);
        int EVP_PKEY_CTX_set_rsa_pss_saltlen(EVP_PKEY_CTX *ctx, int len);
        int EVP_PKEY_CTX_set_rsa_rsa_keygen_bits(EVP_PKEY_CTX *ctx, int mbits);
        int EVP_PKEY_CTX_set_rsa_keygen_pubexp(EVP_PKEY_CTX *ctx, BIGNUM *pubexp);

        #include <openssl/dsa.h>
        int EVP_PKEY_CTX_set_dsa_paramgen_bits(EVP_PKEY_CTX *ctx, int nbits);

        #include <openssl/dh.h>
        int EVP_PKEY_CTX_set_dh_paramgen_prime_len(EVP_PKEY_CTX *ctx, int len);
        int EVP_PKEY_CTX_set_dh_paramgen_generator(EVP_PKEY_CTX *ctx, int gen);

        #include <openssl/ec.h>
        int EVP_PKEY_CTX_set_ec_paramgen_curve_nid(EVP_PKEY_CTX *ctx, int nid);

DESCRIPTION

       The function EVP_PKEY_CTX_ctrl() sends a control operation to the context ctx. The key
       type used must match keytype if it is not -1. The parameter optype is a mask indicating
       which operations the control can be applied to.  The control command is indicated in cmd
       and any additional arguments in p1 and p2.

       Applications will not normally call EVP_PKEY_CTX_ctrl() directly but will instead call one
       of the algorithm specific macros below.

       The function EVP_PKEY_ctrl_str() allows an application to send an algorithm specific
       control operation to a context ctx in string form. This is intended to be used for options
       specified on the command line or in text files. The commands supported are documented in
       the openssl utility command line pages for the option -pkeyopt which is supported by the
       pkeyutl, genpkey and req commands.

       All the remaining "functions" are implemented as macros.

       The EVP_PKEY_CTX_set_signature_md() macro sets the message digest type used in a
       signature. It can be used with any public key algorithm supporting signature operations.

       The macro EVP_PKEY_CTX_set_rsa_padding() sets the RSA padding mode for ctx.  The pad
       parameter can take the value RSA_PKCS1_PADDING for PKCS#1 padding, RSA_SSLV23_PADDING for
       SSLv23 padding, RSA_NO_PADDING for no padding, RSA_PKCS1_OAEP_PADDING for OAEP padding
       (encrypt and decrypt only), RSA_X931_PADDING for X9.31 padding (signature operations only)
       and RSA_PKCS1_PSS_PADDING (sign and verify only).

       Two RSA padding modes behave differently if EVP_PKEY_CTX_set_signature_md() is used. If
       this macro is called for PKCS#1 padding the plaintext buffer is an actual digest value and
       is encapsulated in a DigestInfo structure according to PKCS#1 when signing and this
       structure is expected (and stripped off) when verifying. If this control is not used with
       RSA and PKCS#1 padding then the supplied data is used directly and not encapsulated. In
       the case of X9.31 padding for RSA the algorithm identifier byte is added or checked and
       removed if this control is called. If it is not called then the first byte of the
       plaintext buffer is expected to be the algorithm identifier byte.

       The EVP_PKEY_CTX_set_rsa_pss_saltlen() macro sets the RSA PSS salt length to len as its
       name implies it is only supported for PSS padding.  Two special values are supported: -1
       sets the salt length to the digest length. When signing -2 sets the salt length to the
       maximum permissible value. When verifying -2 causes the salt length to be automatically
       determined based on the PSS block structure. If this macro is not called a salt length
       value of -2 is used by default.

       The EVP_PKEY_CTX_set_rsa_rsa_keygen_bits() macro sets the RSA key length for RSA key
       genration to bits. If not specified 1024 bits is used.

       The EVP_PKEY_CTX_set_rsa_keygen_pubexp() macro sets the public exponent value for RSA key
       generation to pubexp currently it should be an odd integer. The pubexp pointer is used
       internally by this function so it should not be modified or free after the call. If this
       macro is not called then 65537 is used.

       The macro EVP_PKEY_CTX_set_dsa_paramgen_bits() sets the number of bits used for DSA
       parameter generation to bits. If not specified 1024 is used.

       The macro EVP_PKEY_CTX_set_dh_paramgen_prime_len() sets the length of the DH prime
       parameter p for DH parameter generation. If this macro is not called then 1024 is used.

       The EVP_PKEY_CTX_set_dh_paramgen_generator() macro sets DH generator to gen for DH
       parameter generation. If not specified 2 is used.

       The EVP_PKEY_CTX_set_ec_paramgen_curve_nid() sets the EC curve for EC parameter generation
       to nid. For EC parameter generation this macro must be called or an error occurs because
       there is no default curve.

RETURN VALUES

       EVP_PKEY_CTX_ctrl() and its macros return a positive value for success and 0 or a negative
       value for failure. In particular a return value of -2 indicates the operation is not
       supported by the public key algorithm.

SEE ALSO

       EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3), EVP_PKEY_sign(3),
       EVP_PKEY_verify(3), EVP_PKEY_verify_recover(3), EVP_PKEY_derive(3) EVP_PKEY_keygen(3)

HISTORY

       These functions were first added to OpenSSL 1.0.0.