- NAME
- SYNOPSIS
- DESCRIPTION

- RSA parameters
- DSA parameters
- DH parameters
- DH key derivation function parameters
- EC parameters
- ECDH parameters
- ECDH key derivation function parameters
- Other parameters

- RETURN VALUES
- SEE ALSO
- HISTORY
- COPYRIGHT

# NAME

EVP_PKEY_CTX_get_params, EVP_PKEY_CTX_gettable_params, EVP_PKEY_CTX_set_params, EVP_PKEY_CTX_settable_params, EVP_PKEY_CTX_ctrl, EVP_PKEY_CTX_ctrl_str, EVP_PKEY_CTX_ctrl_uint64, EVP_PKEY_CTX_md, 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_get_rsa_padding, EVP_PKEY_CTX_set_rsa_pss_saltlen, EVP_PKEY_CTX_get_rsa_pss_saltlen, EVP_PKEY_CTX_set_rsa_keygen_bits, EVP_PKEY_CTX_set_rsa_keygen_pubexp, EVP_PKEY_CTX_set_rsa_keygen_primes, EVP_PKEY_CTX_set_rsa_mgf1_md_name, EVP_PKEY_CTX_set_rsa_mgf1_md, EVP_PKEY_CTX_get_rsa_mgf1_md, EVP_PKEY_CTX_get_rsa_mgf1_md_name, EVP_PKEY_CTX_set_rsa_oaep_md_name, EVP_PKEY_CTX_set_rsa_oaep_md, EVP_PKEY_CTX_get_rsa_oaep_md, EVP_PKEY_CTX_get_rsa_oaep_md_name, EVP_PKEY_CTX_set0_rsa_oaep_label, EVP_PKEY_CTX_get0_rsa_oaep_label, EVP_PKEY_CTX_set_dsa_paramgen_bits, EVP_PKEY_CTX_set_dsa_paramgen_q_bits, EVP_PKEY_CTX_set_dsa_paramgen_md, EVP_PKEY_CTX_set_dh_paramgen_prime_len, EVP_PKEY_CTX_set_dh_paramgen_subprime_len, EVP_PKEY_CTX_set_dh_paramgen_generator, EVP_PKEY_CTX_set_dh_paramgen_type, EVP_PKEY_CTX_set_dh_rfc5114, EVP_PKEY_CTX_set_dhx_rfc5114, EVP_PKEY_CTX_set_dh_pad, EVP_PKEY_CTX_set_dh_nid, EVP_PKEY_CTX_set_dh_kdf_type, EVP_PKEY_CTX_get_dh_kdf_type, EVP_PKEY_CTX_set0_dh_kdf_oid, EVP_PKEY_CTX_get0_dh_kdf_oid, EVP_PKEY_CTX_set_dh_kdf_md, EVP_PKEY_CTX_get_dh_kdf_md, EVP_PKEY_CTX_set_dh_kdf_outlen, EVP_PKEY_CTX_get_dh_kdf_outlen, EVP_PKEY_CTX_set0_dh_kdf_ukm, EVP_PKEY_CTX_get0_dh_kdf_ukm, EVP_PKEY_CTX_set_ec_paramgen_curve_nid, EVP_PKEY_CTX_set_ec_param_enc, EVP_PKEY_CTX_set_ecdh_cofactor_mode, EVP_PKEY_CTX_get_ecdh_cofactor_mode, EVP_PKEY_CTX_set_ecdh_kdf_type, EVP_PKEY_CTX_get_ecdh_kdf_type, EVP_PKEY_CTX_set_ecdh_kdf_md, EVP_PKEY_CTX_get_ecdh_kdf_md, EVP_PKEY_CTX_set_ecdh_kdf_outlen, EVP_PKEY_CTX_get_ecdh_kdf_outlen, EVP_PKEY_CTX_set0_ecdh_kdf_ukm, EVP_PKEY_CTX_get0_ecdh_kdf_ukm, 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_get_params(EVP_PKEY_CTX *ctx, OSSL_PARAM *params);
     const OSSL_PARAM *EVP_PKEY_CTX_gettable_params(EVP_PKEY_CTX *ctx);
     int EVP_PKEY_CTX_set_params(EVP_PKEY_CTX *ctx, OSSL_PARAM *params);
     const OSSL_PARAM *EVP_PKEY_CTX_settable_params(EVP_PKEY_CTX *ctx);

     int EVP_PKEY_CTX_ctrl(EVP_PKEY_CTX *ctx, int keytype, int optype,
                           int cmd, int p1, void *p2);
     int EVP_PKEY_CTX_ctrl_uint64(EVP_PKEY_CTX *ctx, int keytype, int optype,
                                  int cmd, uint64_t value);
     int EVP_PKEY_CTX_ctrl_str(EVP_PKEY_CTX *ctx, const char *type,
                               const char *value);

     int EVP_PKEY_CTX_md(EVP_PKEY_CTX *ctx, int optype, int cmd, const char *md);

     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, const 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_get_rsa_padding(EVP_PKEY_CTX *ctx, int *pad);
     int EVP_PKEY_CTX_set_rsa_pss_saltlen(EVP_PKEY_CTX *ctx, int saltlen);
     int EVP_PKEY_CTX_get_rsa_pss_saltlen(EVP_PKEY_CTX *ctx, int *saltlen);
     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);
     int EVP_PKEY_CTX_set_rsa_keygen_primes(EVP_PKEY_CTX *ctx, int primes);
     int EVP_PKEY_CTX_set_rsa_mgf1_md_name(EVP_PKEY_CTX *ctx, const char *mdname,
                                         const char *mdprops);
     int EVP_PKEY_CTX_set_rsa_mgf1_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);
     int EVP_PKEY_CTX_get_rsa_mgf1_md(EVP_PKEY_CTX *ctx, const EVP_MD **md);
     int EVP_PKEY_CTX_get_rsa_mgf1_md_name(EVP_PKEY_CTX *ctx, char *name,
                                           size_t namelen);
     int EVP_PKEY_CTX_set_rsa_oaep_md_name(EVP_PKEY_CTX *ctx, const char *mdname,
                                           const char *mdprops);
     int EVP_PKEY_CTX_set_rsa_oaep_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);
     int EVP_PKEY_CTX_get_rsa_oaep_md(EVP_PKEY_CTX *ctx, const EVP_MD **md);
     int EVP_PKEY_CTX_get_rsa_oaep_md_name(EVP_PKEY_CTX *ctx, char *name,
                                           size_t namelen)
     int EVP_PKEY_CTX_set0_rsa_oaep_label(EVP_PKEY_CTX *ctx, unsigned char *label, int len);
     int EVP_PKEY_CTX_get0_rsa_oaep_label(EVP_PKEY_CTX *ctx, unsigned char **label);

     #include <openssl/dsa.h>

     int EVP_PKEY_CTX_set_dsa_paramgen_bits(EVP_PKEY_CTX *ctx, int nbits);
     int EVP_PKEY_CTX_set_dsa_paramgen_q_bits(EVP_PKEY_CTX *ctx, int qbits);
     int EVP_PKEY_CTX_set_dsa_paramgen_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);

     #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_subprime_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_paramgen_type(EVP_PKEY_CTX *ctx, int type);
     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);
     int EVP_PKEY_CTX_set_dh_rfc5114(EVP_PKEY_CTX *ctx, int rfc5114);
     int EVP_PKEY_CTX_set_dhx_rfc5114(EVP_PKEY_CTX *ctx, int rfc5114);
     int EVP_PKEY_CTX_set_dh_kdf_type(EVP_PKEY_CTX *ctx, int kdf);
     int EVP_PKEY_CTX_get_dh_kdf_type(EVP_PKEY_CTX *ctx);
     int EVP_PKEY_CTX_set0_dh_kdf_oid(EVP_PKEY_CTX *ctx, ASN1_OBJECT *oid);
     int EVP_PKEY_CTX_get0_dh_kdf_oid(EVP_PKEY_CTX *ctx, ASN1_OBJECT **oid);
     int EVP_PKEY_CTX_set_dh_kdf_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);
     int EVP_PKEY_CTX_get_dh_kdf_md(EVP_PKEY_CTX *ctx, const EVP_MD **md);
     int EVP_PKEY_CTX_set_dh_kdf_outlen(EVP_PKEY_CTX *ctx, int len);
     int EVP_PKEY_CTX_get_dh_kdf_outlen(EVP_PKEY_CTX *ctx, int *len);
     int EVP_PKEY_CTX_set0_dh_kdf_ukm(EVP_PKEY_CTX *ctx, unsigned char *ukm, int len);
     int EVP_PKEY_CTX_get0_dh_kdf_ukm(EVP_PKEY_CTX *ctx, unsigned char **ukm);

     #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_set_ecdh_cofactor_mode(EVP_PKEY_CTX *ctx, int cofactor_mode);
     int EVP_PKEY_CTX_get_ecdh_cofactor_mode(EVP_PKEY_CTX *ctx);
     int EVP_PKEY_CTX_set_ecdh_kdf_type(EVP_PKEY_CTX *ctx, int kdf);
     int EVP_PKEY_CTX_get_ecdh_kdf_type(EVP_PKEY_CTX *ctx);
     int EVP_PKEY_CTX_set_ecdh_kdf_md(EVP_PKEY_CTX *ctx, const EVP_MD *md);
     int EVP_PKEY_CTX_get_ecdh_kdf_md(EVP_PKEY_CTX *ctx, const EVP_MD **md);
     int EVP_PKEY_CTX_set_ecdh_kdf_outlen(EVP_PKEY_CTX *ctx, int len);
     int EVP_PKEY_CTX_get_ecdh_kdf_outlen(EVP_PKEY_CTX *ctx, int *len);
     int EVP_PKEY_CTX_set0_ecdh_kdf_ukm(EVP_PKEY_CTX *ctx, unsigned char *ukm, int len);
     int EVP_PKEY_CTX_get0_ecdh_kdf_ukm(EVP_PKEY_CTX *ctx, unsigned char **ukm);

     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 `EVP_PKEY_CTX_get_params()` and `EVP_PKEY_CTX_set_params()` functions get and send arbitrary parameters from and to the algorithm implementation respectively. Not all parameters may be supported by all providers. See OSSL_PROVIDER(3) for more information on providers. See OSSL_PARAM(3) for more information on parameters. These functions must only be called after the EVP_PKEY_CTX has been initialised for use in an operation.

The parameters currently supported by the default provider are:

"pad" (OSSL_EXCHANGE_PARAM_PAD) <unsigned integer>

  Sets the DH padding mode. If OSSL_EXCHANGE_PARAM_PAD is 1 then the shared secret is padded with zeros up to the size of the DH prime p. If OSSL_EXCHANGE_PARAM_PAD is zero (the default) then no padding is performed.

"digest" (OSSL_SIGNATURE_PARAM_DIGEST) <UTF8 string>

  Gets and sets the name of the digest algorithm used for the input to the signature functions.

"digest-size" (OSSL_SIGNATURE_PARAM_DIGEST_SIZE) <unsigned integer>

  Gets and sets the output size of the digest algorithm used for the input to the signature functions. The length of the "digest-size" parameter should not exceed that of a size_t. The internal algorithm that supports this parameter is DSA.

`EVP_PKEY_CTX_gettable_params()` and `EVP_PKEY_CTX_settable_params()` gets a constant OSSL_PARAM array that describes the gettable and settable parameters for the current algorithm implementation, i.e. parameters that can be used with `EVP_PKEY_CTX_get_params()` and `EVP_PKEY_CTX_set_params()` respectively. See OSSL_PARAM(3) for the use of OSSL_PARAM as parameter descriptor. These functions must only be called after the EVP_PKEY_CTX has been initialised for use in an operation.

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 the 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_uint64() is a wrapper that directly passes a uint64 value as p2 to `EVP_PKEY_CTX_ctrl()`.

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.

The function `EVP_PKEY_CTX_md()` sends a message digest control operation to the context ctx. The message digest is specified by its name md.

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

All the remaining "functions" are implemented as macros.

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.

## RSA parameters

The `EVP_PKEY_CTX_set_rsa_padding()` function 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), RSA_PKCS1_PSS_PADDING (sign and verify only) and RSA_PKCS1_WITH_TLS_PADDING for TLS RSA ClientKeyExchange message padding (decryption 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_get_rsa_padding()` function gets the RSA padding mode for ctx.

The `EVP_PKEY_CTX_set_rsa_pss_saltlen()` function sets the RSA PSS salt length to saltlen. As its name implies it is only supported for PSS padding. If this function is not called then the maximum salt length is used when signing and auto detection when verifying. 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.

RSA_PSS_SALTLEN_AUTO

  causes the salt length to be automatically determined based on the PSS block structure when verifying. When signing, it has the same meaning as RSA_PSS_SALTLEN_MAX.

The `EVP_PKEY_CTX_get_rsa_pss_saltlen()` function gets the RSA PSS salt length for ctx. The padding mode must already have been set to RSA_PKCS1_PSS_PADDING.

The `EVP_PKEY_CTX_set_rsa_keygen_bits()` macro sets the RSA key length for RSA key generation to bits. If not specified 2048 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 freed after the call. If not specified 65537 is used.

The `EVP_PKEY_CTX_set_rsa_keygen_primes()` macro sets the number of primes for RSA key generation to primes. If not specified 2 is used.

The EVP_PKEY_CTX_set_rsa_mgf1_md_name() function sets the MGF1 digest for RSA padding schemes to the digest named mdname. If the RSA algorithm implementation for the selected provider supports it then the digest will be fetched using the properties mdprops. If not explicitly set the signing digest is used. The padding mode must have been set to RSA_PKCS1_OAEP_PADDING or RSA_PKCS1_PSS_PADDING.

The EVP_PKEY_CTX_set_rsa_mgf1_md() function does the same as EVP_PKEY_CTX_set_rsa_mgf1_md_name() except that the name of the digest is inferred from the supplied md and it is not possible to specify any properties.

The EVP_PKEY_CTX_get_rsa_mgf1_md_name() function gets the name of the MGF1 digest algorithm for ctx. If not explicitly set the signing digest is used. The padding mode must have been set to RSA_PKCS1_OAEP_PADDING or RSA_PKCS1_PSS_PADDING.

The EVP_PKEY_CTX_get_rsa_mgf1_md() function does the same as EVP_PKEY_CTX_get_rsa_mgf1_md_name() except that it returns a pointer to an EVP_MD object instead. Note that only known, built-in EVP_MD objects will be returned. The EVP_MD object may be NULL if the digest is not one of these (such as a digest only implemented in a third party provider).

The `EVP_PKEY_CTX_set_rsa_oaep_md_name()` function sets the message digest type used in RSA OAEP to the digest named mdname. If the RSA algorithm implementation for the selected provider supports it then the digest will be fetched using the properties mdprops. The padding mode must have been set to RSA_PKCS1_OAEP_PADDING.

The `EVP_PKEY_CTX_set_rsa_oaep_md()` function does the same as `EVP_PKEY_CTX_set_rsa_oaep_md_name()` except that the name of the digest is inferred from the supplied md and it is not possible to specify any properties.

The `EVP_PKEY_CTX_get_rsa_oaep_md_name()` function gets the message digest algorithm name used in RSA OAEP and stores it in the buffer name which is of size namelen. The padding mode must have been set to RSA_PKCS1_OAEP_PADDING. The buffer should be sufficiently large for any expected digest algorithm names or the function will fail.

The `EVP_PKEY_CTX_get_rsa_oaep_md()` function does the same as `EVP_PKEY_CTX_get_rsa_oaep_md_name()` except that it returns a pointer to an EVP_MD object instead. Note that only known, built-in EVP_MD objects will be returned. The EVP_MD object may be NULL if the digest is not one of these (such as a digest only implemented in a third party provider).

The EVP_PKEY_CTX_set0_rsa_oaep_label() function sets the RSA OAEP label to label and its length to len. If label is NULL or len is 0, the label is cleared. The library takes ownership of the label so the caller should not free the original memory pointed to by label. The padding mode must have been set to RSA_PKCS1_OAEP_PADDING.

The EVP_PKEY_CTX_get0_rsa_oaep_label() function gets the RSA OAEP label to label. The return value is the label length. The padding mode must have been set to RSA_PKCS1_OAEP_PADDING. The resulting pointer is owned by the library and should not be freed by the caller.

RSA_PKCS1_WITH_TLS_PADDING is used when decrypting an RSA encrypted TLS pre-master secret in a TLS ClientKeyExchange message. It is the same as RSA_PKCS1_PADDING except that it additionally verifies that the result is the correct length and the first two bytes are the protocol version initially requested by the client. If the encrypted content is publicly invalid then the decryption will fail. However, if the padding checks fail then decryption will still appear to succeed but a random TLS premaster secret will be returned instead. This padding mode accepts two parameters which can be set using the EVP_PKEY_CTX_set_params(3) function. These are OSSL_ASYM_CIPHER_PARAM_TLS_CLIENT_VERSION and OSSL_ASYM_CIPHER_PARAM_TLS_NEGOTIATED_VERSION, both of which are expected to be unsigned integers. Normally only the first of these will be set and represents the TLS protocol version that was first requested by the client (e.g. 0x0303 for TLSv1.2, 0x0302 for TLSv1.1 etc). Historically some buggy clients would use the negotiated protocol version instead of the protocol version first requested. If this behaviour should be tolerated then OSSL_ASYM_CIPHER_PARAM_TLS_NEGOTIATED_VERSION should be set to the actual negotiated protocol version. Otherwise it should be left unset.

## DSA parameters

The `EVP_PKEY_CTX_set_dsa_paramgen_bits()` macro sets the number of bits used for DSA parameter generation to nbits. If not specified, 2048 is used.

The `EVP_PKEY_CTX_set_dsa_paramgen_q_bits()` macro sets the number of bits in the subprime parameter q for DSA parameter generation to qbits. If not specified, 224 is used. If a digest function is specified below, this parameter is ignored and instead, the number of bits in q matches the size of the digest.

The `EVP_PKEY_CTX_set_dsa_paramgen_md()` macro sets the digest function used for DSA parameter generation to md. If not specified, one of SHA-1, SHA-224, or SHA-256 is selected to match the bit length of q above.

## DH parameters

The `EVP_PKEY_CTX_set_dh_paramgen_prime_len()` macro sets the length of the DH prime parameter p for DH parameter generation. If this macro is not called then 2048 is used. Only accepts lengths greater than or equal to 256.

The `EVP_PKEY_CTX_set_dh_paramgen_subprime_len()` macro sets the length of the DH optional subprime parameter q for DH parameter generation. The default is 256 if the prime is at least 2048 bits long or 160 otherwise. The DH paramgen type must have been set to DH_PARAMGEN_TYPE_FIPS_186_2 or DH_PARAMGEN_TYPE_FIPS_186_4.

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_paramgen_type()` macro sets the key type for DH parameter generation. The supported parameters are:

DH_PARAMGEN_TYPE_GENERATOR

  Uses a generator g (PKCS#3 format).

DH_PARAMGEN_TYPE_FIPS_186_2

  FIPS186-2 FFC parameter generator (X9.42 DH).

DH_PARAMGEN_TYPE_FIPS_186_4

  FIPS186-4 FFC parameter generator.

The default is DH_PARAMGEN_TYPE_GENERATOR.

The `EVP_PKEY_CTX_set_dh_pad()` function sets the DH padding mode. If pad is 1 the shared secret is padded with zeros 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 as defined in RFC7919 or RFC3526. The nid parameter must be NID_ffdhe2048, NID_ffdhe3072, NID_ffdhe4096, NID_ffdhe6144, NID_ffdhe8192, NID_modp_1536, NID_modp_2048, NID_modp_3072, NID_modp_4096, NID_modp_6144, NID_modp_8192 or NID_undef to clear the stored value. This macro can be called during parameter or key generation. The nid parameter and the rfc5114 parameter are mutually exclusive.

The EVP_PKEY_CTX_set_dh_rfc5114() and EVP_PKEY_CTX_set_dhx_rfc5114() macros are synonymous. They set the DH parameters to the values defined in RFC5114. The rfc5114 parameter must be 1, 2 or 3 corresponding to RFC5114 sections 2.1, 2.2 and 2.3. or 0 to clear the stored value. This macro can be called during parameter generation. The ctx must have a key type of EVP_PKEY_DHX. The rfc5114 parameter and the nid parameter are mutually exclusive.

## DH key derivation function parameters

Note that all of the following functions require that the ctx parameter has a private key type of EVP_PKEY_DHX. When using key derivation, the output of `EVP_PKEY_derive()` is the output of the KDF instead of the DH shared secret. The KDF output is typically used as a Key Encryption Key (KEK) that in turn encrypts a Content Encryption Key (CEK).

The `EVP_PKEY_CTX_set_dh_kdf_type()` macro sets the key derivation function type to kdf for DH key derivation. Possible values are EVP_PKEY_DH_KDF_NONE and EVP_PKEY_DH_KDF_X9_42 which uses the key derivation specified in RFC2631 (based on the keying algorithm described in X9.42). When using key derivation, the kdf_oid, kdf_md and kdf_outlen parameters must also be specified.

The `EVP_PKEY_CTX_get_dh_kdf_type()` macro gets the key derivation function type for ctx used for DH key derivation. Possible values are EVP_PKEY_DH_KDF_NONE and EVP_PKEY_DH_KDF_X9_42.

The EVP_PKEY_CTX_set0_dh_kdf_oid() macro sets the key derivation function object identifier to oid for DH key derivation. This OID should identify the algorithm to be used with the Content Encryption Key. The library takes ownership of the object identifier so the caller should not free the original memory pointed to by oid.

The EVP_PKEY_CTX_get0_dh_kdf_oid() macro gets the key derivation function oid for ctx used for DH key derivation. The resulting pointer is owned by the library and should not be freed by the caller.

The `EVP_PKEY_CTX_set_dh_kdf_md()` macro sets the key derivation function message digest to md for DH key derivation. Note that RFC2631 specifies that this digest should be SHA1 but OpenSSL tolerates other digests.

The `EVP_PKEY_CTX_get_dh_kdf_md()` macro gets the key derivation function message digest for ctx used for DH key derivation.

The `EVP_PKEY_CTX_set_dh_kdf_outlen()` macro sets the key derivation function output length to len for DH key derivation.

The `EVP_PKEY_CTX_get_dh_kdf_outlen()` macro gets the key derivation function output length for ctx used for DH key derivation.

The EVP_PKEY_CTX_set0_dh_kdf_ukm() macro sets the user key material to ukm and its length to len for DH key derivation. This parameter is optional and corresponds to the partyAInfo field in RFC2631 terms. The specification requires that it is 512 bits long but this is not enforced by OpenSSL. The library takes ownership of the user key material so the caller should not free the original memory pointed to by ukm.

The EVP_PKEY_CTX_get0_dh_kdf_ukm() macro gets the user key material for ctx. The return value is the user key material length. The resulting pointer is owned by the library and should not be freed by the caller.

## EC parameters

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()` macro 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 added in OpenSSL 1.1.0; previous versions should use 0 instead.

## ECDH parameters

The `EVP_PKEY_CTX_set_ecdh_cofactor_mode()` macro sets the cofactor mode to cofactor_mode for ECDH key derivation. Possible values are 1 to enable cofactor key derivation, 0 to disable it and -1 to clear the stored cofactor mode and fallback to the private key cofactor mode.

The `EVP_PKEY_CTX_get_ecdh_cofactor_mode()` macro returns the cofactor mode for ctx used for ECDH key derivation. Possible values are 1 when cofactor key derivation is enabled and 0 otherwise.

## ECDH key derivation function parameters

The `EVP_PKEY_CTX_set_ecdh_kdf_type()` macro sets the key derivation function type to kdf for ECDH key derivation. Possible values are EVP_PKEY_ECDH_KDF_NONE and EVP_PKEY_ECDH_KDF_X9_63 which uses the key derivation specified in X9.63. When using key derivation, the kdf_md and kdf_outlen parameters must also be specified.

The `EVP_PKEY_CTX_get_ecdh_kdf_type()` macro returns the key derivation function type for ctx used for ECDH key derivation. Possible values are EVP_PKEY_ECDH_KDF_NONE and EVP_PKEY_ECDH_KDF_X9_63.

The `EVP_PKEY_CTX_set_ecdh_kdf_md()` macro sets the key derivation function message digest to md for ECDH key derivation. Note that X9.63 specifies that this digest should be SHA1 but OpenSSL tolerates other digests.

The `EVP_PKEY_CTX_get_ecdh_kdf_md()` macro gets the key derivation function message digest for ctx used for ECDH key derivation.

The `EVP_PKEY_CTX_set_ecdh_kdf_outlen()` macro sets the key derivation function output length to len for ECDH key derivation.

The `EVP_PKEY_CTX_get_ecdh_kdf_outlen()` macro gets the key derivation function output length for ctx used for ECDH key derivation.

The EVP_PKEY_CTX_set0_ecdh_kdf_ukm() macro sets the user key material to ukm for ECDH key derivation. This parameter is optional and corresponds to the shared info in X9.63 terms. The library takes ownership of the user key material so the caller should not free the original memory pointed to by ukm.

The EVP_PKEY_CTX_get0_ecdh_kdf_ukm() macro gets the user key material for ctx. The return value is the user key material length. The resulting pointer is owned by the library and should not be freed by the caller.

## Other parameters

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_set_params()` returns 1 for success or 0 otherwise. `EVP_PKEY_CTX_settable_params()` returns an OSSL_PARAM array on success or NULL on error. It may also return NULL if there are no settable parameters available.

All other functions and macros described on this page 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_get_signature_md()`, `EVP_PKEY_CTX_set_signature_md()`, `EVP_PKEY_CTX_set_dh_pad()`, `EVP_PKEY_CTX_set_rsa_padding()`, `EVP_PKEY_CTX_get_rsa_padding()`, EVP_PKEY_CTX_get_rsa_mgf1_md(), EVP_PKEY_CTX_set_rsa_mgf1_md(), `EVP_PKEY_CTX_set_rsa_oaep_md()`, `EVP_PKEY_CTX_get_rsa_oaep_md()`, EVP_PKEY_CTX_set0_rsa_oaep_label(), EVP_PKEY_CTX_get0_rsa_oaep_label(), `EVP_PKEY_CTX_set_rsa_pss_saltlen()`, `EVP_PKEY_CTX_get_rsa_pss_saltlen()`, were macros in OpenSSL 1.1.1 and below. From OpenSSL 3.0 they are functions.

`EVP_PKEY_CTX_get_rsa_oaep_md_name()`, EVP_PKEY_CTX_get_rsa_mgf1_md_name(), EVP_PKEY_CTX_set_rsa_mgf1_md_name() and `EVP_PKEY_CTX_set_rsa_oaep_md_name()` were added in OpenSSL 3.0.

The 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 added in OpenSSL 1.0.0.

# COPYRIGHT

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

Licensed under the Apache License 2.0 (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.