EVP_PKEY_CTX_CTRL(3)

NAME
EVP_PKEY_CTX_ctrl, EVP_PKEY_CTX_ctrl_str, EVP_PKEY_CTX_set_signature_md, EVP_PKEY_CTX_get_signature_md, EVP_PKEY_CTX_set_mac_key, EVP_PKEY_CTX_set_rsa_padding, EVP_PKEY_CTX_set_rsa_pss_saltlen, EVP_PKEY_CTX_set_rsa_keygen_bits, EVP_PKEY_CTX_set_rsa_keygen_pubexp, EVP_PKEY_CTX_set_dsa_paramgen_bits, EVP_PKEY_CTX_set_dh_paramgen_prime_len, EVP_PKEY_CTX_set_dh_paramgen_generator, EVP_PKEY_CTX_set_dh_pad, EVP_PKEY_CTX_set_dh_nid, EVP_PKEY_CTX_set_ec_paramgen_curve_nid, EVP_PKEY_CTX_set_ec_param_enc, EVP_PKEY_CTX_set1_id, EVP_PKEY_CTX_get1_id, EVP_PKEY_CTX_get1_id_len - 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_CTX_set_signature_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);
 int EVP_PKEY_CTX_get_signature_md(EVP_PKEY_CTX *ctx, const EVP_MD **pmd);

 int EVP_PKEY_CTX_set_mac_key(EVP_PKEY_CTX *ctx, unsigned char *key, int len);

 #include <openssl/rsa.h>

 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_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);
 int EVP_PKEY_CTX_set_dh_pad(EVP_PKEY_CTX *ctx, int pad);
 int EVP_PKEY_CTX_set_dh_nid(EVP_PKEY_CTX *ctx, int nid);

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

 int EVP_PKEY_CTX_set1_id(EVP_PKEY_CTX *ctx, void *id, size_t id_len);
 int EVP_PKEY_CTX_get1_id(EVP_PKEY_CTX *ctx, void *id);
 int EVP_PKEY_CTX_get1_id_len(EVP_PKEY_CTX *ctx, size_t *id_len);

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.

For cmd = EVP_PKEY_CTRL_SET_MAC_KEY, p1 is the length of the MAC key, and p2 is MAC key. This is used by Poly1305, SipHash, HMAC and CMAC.

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_CTX_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 in the RSA, DSA and ECDSA algorithms.

The EVP_PKEY_CTX_get_signature_md() macro gets the message digest type used in a signature. It can be used in the RSA, DSA and ECDSA algorithms.

Key generation typically involves setting up parameters to be used and generating the private and public key data. Some algorithm implementations allow private key data to be set explicitly using the EVP_PKEY_CTX_set_mac_key() macro. In this case key generation is simply the process of setting up the parameters for the key and then setting the raw key data to the value explicitly provided by that macro. Normally applications would call EVP_PKEY_new_raw_private_key(3) or similar functions instead of this macro.

The EVP_PKEY_CTX_set_mac_key() macro can be used with any of the algorithms supported by the EVP_PKEY_new_raw_private_key(3) function.

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. Three special values are supported: RSA_PSS_SALTLEN_DIGEST sets the salt length to the digest length, RSA_PSS_SALTLEN_MAX sets the salt length to the maximum permissible value. When verifying RSA_PSS_SALTLEN_AUTO causes the salt length to be automatically determined based on the PSS block structure. If this macro is not called maximum salt length is used when signing and auto detection when verifying is used by default.

The EVP_PKEY_CTX_set_rsa_keygen_bits() macro sets the RSA key length for RSA key generation 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_dh_pad() macro sets the DH padding mode. If pad is 1 the shared secret is padded with zeroes up to the size of the DH prime p. If pad is zero (the default) then no padding is performed.

EVP_PKEY_CTX_set_dh_nid() sets the DH parameters to values corresponding to nid. The nid parameter must be NID_ffdhe2048, NID_ffdhe3072, NID_ffdhe4096, NID_ffdhe6144 or NID_ffdhe8192. This macro can be called during parameter or key generation.

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. This function can also be called to set the curve explicitly when generating an EC key.

The EVP_PKEY_CTX_set_ec_param_enc() sets the EC parameter encoding to param_enc when generating EC parameters or an EC key. The encoding can be OPENSSL_EC_EXPLICIT_CURVE for explicit parameters (the default in versions of OpenSSL before 1.1.0) or OPENSSL_EC_NAMED_CURVE to use named curve form. For maximum compatibility the named curve form should be used. Note: the OPENSSL_EC_NAMED_CURVE value was only added to OpenSSL 1.1.0; previous versions should use 0 instead.

The EVP_PKEY_CTX_set1_id(), EVP_PKEY_CTX_get1_id() and EVP_PKEY_CTX_get1_id_len() macros are used to manipulate the special identifier field for specific signature algorithms such as SM2. The EVP_PKEY_CTX_set1_id() sets an ID pointed by id with the length id_len to the library. The library takes a copy of the id so that the caller can safely free the original memory pointed to by id. The EVP_PKEY_CTX_get1_id_len() macro returns the length of the ID set via a previous call to EVP_PKEY_CTX_set1_id(). The length is usually used to allocate adequate memory for further calls to EVP_PKEY_CTX_get1_id(). The EVP_PKEY_CTX_get1_id() macro returns the previously set ID value to caller in id. The caller should allocate adequate memory space for the id before calling EVP_PKEY_CTX_get1_id().

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
EVP_PKEY_CTX_set1_id(), EVP_PKEY_CTX_get1_id() and EVP_PKEY_CTX_get1_id_len() macros were added in 1.1.1, other functions were first added to OpenSSL 1.0.0.

COPYRIGHT
Copyright 2006-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.