EVP_PKEY_CTX_CTRL(3SSL)
💖 EVP_PKEY_CTX_CTRL — algorithm specific control operations 💖
okay bestie, sit down, hydrate, because this is the OpenSSL EVP_PKEY_CTX_CTRL(3SSL) page and it is a whole buffet. this is part one of four, so buckle uppp. it's all the little knobs and dials you can twist on an EVP_PKEY_CTX when you want an algorithm to do something specific. no cap, it's iconic.
✨ NAME ✨
so here's the whole squad of functions this page covers — every single one, i'm not skipping a single bestie:
- core control crew:
EVP_PKEY_CTX_ctrl,EVP_PKEY_CTX_ctrl_str,EVP_PKEY_CTX_ctrl_uint64,EVP_PKEY_CTX_md - signature digest duo:
EVP_PKEY_CTX_set_signature_md,EVP_PKEY_CTX_get_signature_md - key + group stuff:
EVP_PKEY_CTX_set_mac_key,EVP_PKEY_CTX_set_group_name,EVP_PKEY_CTX_get_group_name - KEM:
EVP_PKEY_CTX_set_kem_op - RSA besties:
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_set1_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 - DSA besties:
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_dsa_paramgen_md_props,EVP_PKEY_CTX_set_dsa_paramgen_gindex,EVP_PKEY_CTX_set_dsa_paramgen_type,EVP_PKEY_CTX_set_dsa_paramgen_seed - DH besties:
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_paramgen_gindex,EVP_PKEY_CTX_set_dh_paramgen_seed,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 - EC besties:
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 - identity trio:
EVP_PKEY_CTX_set1_id,EVP_PKEY_CTX_get1_id,EVP_PKEY_CTX_get1_id_len
— algorithm specific control operations 🎀
✨ SYNOPSIS ✨
first, the include, obviously:
#include <openssl/evp.h>then the general-purpose control functions, she's versatile:
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);
int EVP_PKEY_CTX_set_group_name(EVP_PKEY_CTX *ctx, const char *name);
int EVP_PKEY_CTX_get_group_name(EVP_PKEY_CTX *ctx, char *name, size_t namelen);
int EVP_PKEY_CTX_set_kem_op(EVP_PKEY_CTX *ctx, const char *op);now the RSA section, grab <openssl/rsa.h>:
#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_set1_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, void *label,
int len);
int EVP_PKEY_CTX_get0_rsa_oaep_label(EVP_PKEY_CTX *ctx, unsigned char **label);DSA, <openssl/dsa.h>:
#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);
int EVP_PKEY_CTX_set_dsa_paramgen_md_props(EVP_PKEY_CTX *ctx,
const char *md_name,
const char *md_properties);
int EVP_PKEY_CTX_set_dsa_paramgen_type(EVP_PKEY_CTX *ctx, const char *name);
int EVP_PKEY_CTX_set_dsa_paramgen_gindex(EVP_PKEY_CTX *ctx, int gindex);
int EVP_PKEY_CTX_set_dsa_paramgen_seed(EVP_PKEY_CTX *ctx,
const unsigned char *seed,
size_t seedlen);DH, <openssl/dh.h>:
#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_paramgen_gindex(EVP_PKEY_CTX *ctx, int gindex);
int EVP_PKEY_CTX_set_dh_paramgen_seed(EVP_PKEY_CTX *ctx,
const unsigned char *seed,
size_t seedlen);
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);EC, <openssl/ec.h>:
#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);and the identity functions, back in <openssl/evp.h> territory:
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);🚫 the deprecated girlies 🚫
these following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):
#include <openssl/rsa.h>
int EVP_PKEY_CTX_set_rsa_keygen_pubexp(EVP_PKEY_CTX *ctx, BIGNUM *pubexp);#include <openssl/dh.h>
int EVP_PKEY_CTX_get0_dh_kdf_ukm(EVP_PKEY_CTX *ctx, unsigned char **ukm);#include <openssl/ec.h>
int EVP_PKEY_CTX_get0_ecdh_kdf_ukm(EVP_PKEY_CTX *ctx, unsigned char **ukm);⚠️ bestie. deprecated means deprecated. if you're writing new code, don't reach for these. they're giving ✨legacy✨.
✨ DESCRIPTION ✨
okay so. the main character: EVP_PKEY_CTX_ctrl() 💅 she sends a control operation to the context ctx. the key type used must match keytype — unless it's -1, in which case it just matches whatever, we're easy like that. the parameter optype is a mask indicating which operations the control can be applied to. the actual control command goes in cmd, and any extra arguments ride along in p1 and p2. slay.
for cmd = EVP_PKEY_CTRL_SET_MAC_KEY, p1 is the length of the MAC key, and p2 is the MAC key itself. this one is used by Poly1305, SipHash, HMAC and CMAC. so cute of them.
Applications will not normally call EVP_PKEY_CTX_ctrl() directly — instead they'll call one of the algorithm specific functions below. think of her as the backstage manager; the algorithm-specific functions are the ones onstage getting the applause. 🌟
EVP_PKEY_CTX_ctrl_uint64() is a wrapper that directly passes a uint64 value as p2 to EVP_PKEY_CTX_ctrl(). simple, no notes.
EVP_PKEY_CTX_ctrl_str() lets an application 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. yes, the same -pkeyopt you keep copy-pasting from stack overflow. we know. it's giving community. 🫶
EVP_PKEY_CTX_md() sends a message digest control operation to the context ctx. the message digest is specified by its name, md.
EVP_PKEY_CTX_set_signature_md() sets the message digest type used in a signature. she can be used in the RSA, DSA and ECDSA algorithms.
EVP_PKEY_CTX_get_signature_md() gets the message digest type used in a signature. also usable in the RSA, DSA and ECDSA algorithms — the setter's matching bestie.
🔑 key generation vibes 🔑
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 EVP_PKEY_CTX_set_mac_key(). in that 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. normally, applications would call EVP_PKEY_new_raw_private_key(3) or similar functions instead. main character energy, honestly.
EVP_PKEY_CTX_set_mac_key() can be used with any of the algorithms supported by the EVP_PKEY_new_raw_private_key(3) function. choose your fighter. 🌈
okay that's part one, stay tuned because there's SO much more where that came from 💖
EVP_PKEY_CTX_set_group_name() sets the group name to name for parameter and key generation 💫 Like, for EC keys this sets the curve name, and for DH keys it sets the name of the finite field group. Same vibe, different math.
EVP_PKEY_CTX_get_group_name() finds the group name that's currently set with ctx and writes it to the location that name points at — but only if the size namelen is big enough to store that name, including a terminating NUL byte. Ngl, size matters here. Don't skimp on the buffer bestie 💅
🌸 RSA parameters 🌸
EVP_PKEY_CTX_set_rsa_padding()— sets the RSA padding mode forctx. The pad parameter can take these values, and each one has its niche:RSA_PKCS1_PADDING— for PKCS#1 padding 🎀RSA_NO_PADDING— bestie, no padding at all 💀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— PSS padding (sign and verify only!)RSA_PKCS1_WITH_TLS_PADDING— for TLS RSAClientKeyExchangemessage padding (decryption only!)
So listen, two of these RSA padding modes act different if EVP_PKEY_CTX_set_signature_md() gets used 👀 If that function is called for PKCS#1 padding, then the plaintext buffer is an actual digest value and it gets encapsulated in a DigestInfo structure per PKCS#1 when signing — and that structure is expected (and stripped off) when verifying. But if you don't use this control with RSA and PKCS#1 padding, then the supplied data is used directly and not encapsulated, fr fr. And in the X9.31 padding case for RSA, the algorithm identifier byte is added or checked and removed when this control is called. If it's not called, then the first byte of the plaintext buffer is expected to be the algorithm identifier byte. Iconic behaviour honestly ✨
EVP_PKEY_CTX_get_rsa_padding()— gets the RSA padding mode forctx. Just peeking, no cap 🫶EVP_PKEY_CTX_set_rsa_pss_saltlen()— sets the RSA PSS salt length to saltlen. As the name literally implies, it's only supported for PSS padding — no PSS, no service 💅 If this function isn't called, then the salt length is maximized up to the digest length when signing, and auto detection when verifying. There are four special values: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 asRSA_PSS_SALTLEN_MAX.RSA_PSS_SALTLEN_AUTO_DIGEST_MAX— causes the salt length to be automatically determined based on the PSS block structure when verifying, likeRSA_PSS_SALTLEN_AUTO. When signing, the salt length is maximized up to a maximum of the digest length to comply with FIPS 186-4 section 5.5. Compliance queen 👑
EVP_PKEY_CTX_get_rsa_pss_saltlen()— gets the RSA PSS salt length forctx. Heads up though: the padding mode must already have been set toRSA_PKCS1_PSS_PADDINGor it's not gonna work 🙈EVP_PKEY_CTX_set_rsa_keygen_bits()— sets the RSA key length for RSA key generation to bits. If you don't specify it,2048bits is used. Default slay ✨EVP_PKEY_CTX_set1_rsa_keygen_pubexp()— sets the public exponent value for RSA key generation to the value stored in pubexp. Currently it should be an odd integer (yeah, quirky). And per the OpenSSL naming convention, that pubexp pointer must be freed independently of theEVP_PKEY_CTX— because it gets internally copied, bestie, you're not sharing that memory. If not specified,65537is used.EVP_PKEY_CTX_set_rsa_keygen_pubexp()— does the same asEVP_PKEY_CTX_set1_rsa_keygen_pubexp()except there is no internal copy, and therefore pubexp should not be modified or freed after the call ⚠️ Don't touch it, don't free it, just let it vibe.EVP_PKEY_CTX_set_rsa_keygen_primes()— sets the number of primes for RSA key generation to primes. If not specified,2is used.EVP_PKEY_CTX_set_rsa_mgf1_md_name()— 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 toRSA_PKCS1_OAEP_PADDINGorRSA_PKCS1_PSS_PADDING— those are the only two that count 💫EVP_PKEY_CTX_set_rsa_mgf1_md()— does the same asEVP_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. No props, no problem 🎀EVP_PKEY_CTX_get_rsa_mgf1_md_name()— gets the name of the MGF1 digest algorithm forctx. If not explicitly set, the signing digest is used. Padding mode must have been set toRSA_PKCS1_OAEP_PADDINGorRSA_PKCS1_PSS_PADDING.EVP_PKEY_CTX_get_rsa_mgf1_md()— does the same asEVP_PKEY_CTX_get_rsa_mgf1_md_name()except that it returns a pointer to anEVP_MDobject instead. Lowkey important note: only known, built-inEVP_MDobjects will be returned. TheEVP_MDobject may beNULLif the digest isn't one of these — like a digest only implemented in a third party provider 💀EVP_PKEY_CTX_set_rsa_oaep_md_name()— 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 toRSA_PKCS1_OAEP_PADDING.EVP_PKEY_CTX_set_rsa_oaep_md()— does the same asEVP_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.EVP_PKEY_CTX_get_rsa_oaep_md_name()— 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 toRSA_PKCS1_OAEP_PADDING. And btw, that buffer should be sufficiently large for any expected digest algorithm names, or the function will fail 😭 So size it right!EVP_PKEY_CTX_get_rsa_oaep_md()— does the same asEVP_PKEY_CTX_get_rsa_oaep_md_name()except that it returns a pointer to anEVP_MDobject instead. Again, note that only known, built-inEVP_MDobjects will be returned. TheEVP_MDobject may beNULLif the digest is not one of these, like a digest only implemented in a third party provider.EVP_PKEY_CTX_set0_rsa_oaep_label()— sets the RSA OAEP label to binary data label and its length in bytes to len. If label isNULLor len is0, 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 toRSA_PKCS1_OAEP_PADDING.EVP_PKEY_CTX_get0_rsa_oaep_label()— gets the RSA OAEP label to label. The return value is the label length. The padding mode must have been set toRSA_PKCS1_OAEP_PADDING. The resulting pointer is owned by the library and should not be freed by the caller — hands off, bestie 🙅♀️
RSA_PKCS1_WITH_TLS_PADDING is what you use when decrypting an RSA encrypted TLS pre-master secret in a TLS ClientKeyExchange message. It's the same as RSA_PKCS1_PADDING except it additionally verifies that the result is the correct length and that 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 — and this is the spicy part 🌶️ — if the padding checks fail, then decryption will still appear to succeed but a random TLS premaster secret will be returned instead. Sneaky. This padding mode accepts two parameters, which can be set using the EVP_PKEY_CTX_set_params(3) function. Those are OSSL_ASYM_CIPHER_PARAM_TLS_CLIENT_VERSION and OSSL_ASYM_CIPHER_PARAM_TLS_NEGOTIATED_VERSION, and both are expected to be unsigned integers. Normally only the first of these gets set, and it 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 that 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. Periodt.
Similarly to the RSA_PKCS1_WITH_TLS_PADDING above, since OpenSSL version 3.2.0, the use of RSA_PKCS1_PADDING will return a randomly generated message instead of padding errors in case padding checks fail. Applications that want to remain secure while using earlier versions of OpenSSL, or a provider that doesn't implement the implicit rejection mechanism, still need to handle both the error code from the RSA decryption operation and the returned message in a side channel secure manner 🛡️ This protection against Bleichenbacher attacks can be disabled by setting OSSL_ASYM_CIPHER_PARAM_IMPLICIT_REJECTION (an unsigned integer) to 0. Don't do that unless you truly know what you're doing, iykyk 💀
🦋 DSA parameters 🦋
EVP_PKEY_CTX_set_dsa_paramgen_bits()— sets the number of bits used for DSA parameter generation to nbits. If not specified,2048is used.EVP_PKEY_CTX_set_dsa_paramgen_q_bits()— sets the number of bits in the subprime parameter q for DSA parameter generation to qbits. If not specified,224is used. But plot twist: 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 👀EVP_PKEY_CTX_set_dsa_paramgen_md()— sets the digest function used for DSA parameter generation to md. If not specified, one ofSHA-1,SHA-224, orSHA-256is selected to match the bit length of q above.EVP_PKEY_CTX_set_dsa_paramgen_md_props()— sets the digest function used for DSA parameter generation using md_name and md_properties to retrieve the digest from a provider. If not specified, md_name will be set to one ofSHA-1,SHA-224, orSHA-256depending on the bit length of q above. And md_properties is a property query string that has a default value of''if not specified — empty string, no drama 🎀EVP_PKEY_CTX_set_dsa_paramgen_gindex()— sets the gindex used by the generator G. The default value is-1, which uses unverifiable g; otherwise a positive value uses verifiable g ✨ This value must be saved if key validation of g is required, since it is not part of a persisted key. Write it down, bestie 📝EVP_PKEY_CTX_set_dsa_paramgen_seed()— sets the seed to use for generation rather than using a randomly generated value for the seed. This is useful for testing purposes only, and it can fail if the seed does not produce primes for both p & q on its first iteration 🙈 This value must be saved if key validation of p, q, and verifiable g are required, since it is not part of a persisted key.EVP_PKEY_CTX_set_dsa_paramgen_type()— sets the generation type to use: FIPS186-4 generation if name is"fips186_4", or FIPS186-2 generation if name is"fips186_2". The default value for the default provider is"fips186_2". The default value for the FIPS provider is"fips186_4". Know your provider, know your vibe 💅
🌈 DH parameters 🌈
EVP_PKEY_CTX_set_dh_paramgen_prime_len()— sets the length of the DH prime parameter p for DH parameter generation. If this function is not called, then2048is used. Heads up though: it only accepts lengths greater than or equal to256. Anything smaller and it's a no from me ✋
okay bestie</p> we're deep in the DH lore now, stay with me 💖
EVP_PKEY_CTX_set_dh_paramgen_subprime_len()— sets the length of the DH optional subprime parameterqfor DH parameter generation. Default? 256 if the prime is at least 2048 bits long, or 160 otherwise. Heads up tho: the DH paramgen type must have already been set to"fips186_4"or this is giving nothing.EVP_PKEY_CTX_set_dh_paramgen_generator()— sets the DH generator to gen for DH parameter generation. If you don't say anything,2is used. iconic default tbh ✨EVP_PKEY_CTX_set_dh_paramgen_type()— sets the key type for DH parameter generation. The supported parameters are:DH_PARAMGEN_TYPE_GROUP— use a named group. If only the safe prime parameterpis set, this can be used to select a ffdhe safe prime group of the correct size. 💅DH_PARAMGEN_TYPE_FIPS_186_4— FIPS186-4 FFC parameter generator.DH_PARAMGEN_TYPE_FIPS_186_2— FIPS186-2 FFC parameter generator (X9.42 DH).DH_PARAMGEN_TYPE_GENERATOR— uses a safe prime generatorg(PKCS#3 format).
and now the defaults, because they're kinda plot twist: in the default provider the default is DH_PARAMGEN_TYPE_GENERATOR for the "DH" keytype, and DH_PARAMGEN_TYPE_FIPS_186_2 for the "DHX" keytype. In the FIPS provider the default value is DH_PARAMGEN_TYPE_GROUP for the "DH" keytype and <DH_PARAMGEN_TYPE_FIPS_186_4 for the "DHX" keytype.
EVP_PKEY_CTX_set_dh_paramgen_gindex()— sets the gindex used by the generatorG. Default value is-1which uses unverifiableg, otherwise a positive value uses verifiableg. ⚠️ This value must be saved if key validation ofgis required, since it is not part of a persisted key. so don't lose it bestie.EVP_PKEY_CTX_set_dh_paramgen_seed()— sets the seed to use for generation rather than using a randomly generated value for the seed. This is useful for testing purposes only and can fail if the seed does not produce primes for bothp&qon its first iteration. This value must be saved if key validation ofp,q, and verifiablegare required, since it is not part of a persisted key.EVP_PKEY_CTX_set_dh_pad()— sets the DH padding mode. If pad is1the shared secret is padded with zeros up to the size of the DH primep. If pad is zero (the default) then no padding is performed. no padding, no drama 🫶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 beNID_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_8192orNID_undefto clear the stored value. This function can be called during parameter or key generation. The nid parameter and the rfc5114 parameter are mutually exclusive — it's giving pick a lane 💀EVP_PKEY_CTX_set_dh_rfc5114()andEVP_PKEY_CTX_set_dhx_rfc5114()— both set the DH parameters to the values defined in RFC5114. The rfc5114 parameter must be1,2or3corresponding to RFC5114 sections 2.1, 2.2 and 2.3, or0to clear the stored value. This macro can be called during parameter generation. The ctx must have a key type ofEVP_PKEY_DHX. The rfc5114 parameter and the nid parameter are mutually exclusive. (yes, same energy as before, they cannot coexist 💅)
🌸 DH key derivation function parameters 🌸
little note before we go in: 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). nested encryption era 🔥
EVP_PKEY_CTX_set_dh_kdf_type()— sets the key derivation function type to kdf for DH key derivation. Possible values areEVP_PKEY_DH_KDF_NONEandEVP_PKEY_DH_KDF_X9_42which 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. all three, no skipping 🎀EVP_PKEY_CTX_get_dh_kdf_type()— gets the key derivation function type for ctx used for DH key derivation. Possible values areEVP_PKEY_DH_KDF_NONEandEVP_PKEY_DH_KDF_X9_42.EVP_PKEY_CTX_set0_dh_kdf_oid()— 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.EVP_PKEY_CTX_get0_dh_kdf_oid()— 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. hands off bestie 🙈EVP_PKEY_CTX_set_dh_kdf_md()— 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. (tolerant queen 👑)EVP_PKEY_CTX_get_dh_kdf_md()— gets the key derivation function message digest for ctx used for DH key derivation.EVP_PKEY_CTX_set_dh_kdf_outlen()— sets the key derivation function output length to len for DH key derivation.EVP_PKEY_CTX_get_dh_kdf_outlen()— gets the key derivation function output length for ctx used for DH key derivation.EVP_PKEY_CTX_set0_dh_kdf_ukm()— sets the user key material to ukm and its length to len for DH key derivation. This parameter is optional and corresponds to thepartyAInfofield 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.EVP_PKEY_CTX_get0_dh_kdf_ukm()— 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 ✨
Use EVP_PKEY_CTX_set_group_name() (described above, ifykyk) to set the curve name to name for parameter and key generation.
EVP_PKEY_CTX_set_ec_paramgen_curve_nid() does the same as EVP_PKEY_CTX_set_group_name(), but is specific to EC and uses a nid rather than a name string. same vibe, different input 🌈
For EC parameter generation, one of EVP_PKEY_CTX_set_group_name() or EVP_PKEY_CTX_set_ec_paramgen_curve_nid() must be called or an error occurs because there is no default curve. 🚨 These function can also be called to set the curve explicitly when generating an EC key.
EVP_PKEY_CTX_get_group_name() (described above) can be used to obtain the curve name that's currently set with ctx.
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 added in OpenSSL 1.1.0; previous versions should use 0 instead.
🦋 ECDH parameters 🦋
EVP_PKEY_CTX_set_ecdh_cofactor_mode()— sets the cofactor mode to cofactor_mode for ECDH key derivation. Possible values are1to enable cofactor key derivation,0to disable it and-1to clear the stored cofactor mode and fallback to the private key cofactor mode. three modes, three moods 💅EVP_PKEY_CTX_get_ecdh_cofactor_mode()— returns the cofactor mode for ctx used for ECDH key derivation. Possible values are1when cofactor key derivation is enabled and0otherwise.
💜 ECDH key derivation function parameters 💜
EVP_PKEY_CTX_set_ecdh_kdf_type()— sets the key derivation function type to kdf for ECDH key derivation. Possible values areEVP_PKEY_ECDH_KDF_NONEandEVP_PKEY_ECDH_KDF_X9_63which uses the key derivation specified in X9.63. When using key derivation, the kdf_md and kdf_outlen parameters must also be specified. ✨EVP_PKEY_CTX_get_ecdh_kdf_type()— returns the key derivation function type for ctx used for ECDH key derivation. Possible values areEVP_PKEY_ECDH_KDF_NONEandEVP_PKEY_ECDH_KDF_X9_63.EVP_PKEY_CTX_set_ecdh_kdf_md()— 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. again with the tolerance 😭EVP_PKEY_CTX_get_ecdh_kdf_md()— gets the key derivation function message digest for ctx used for ECDH key derivation.EVP_PKEY_CTX_set_ecdh_kdf_outlen()— sets the key derivation function output length to len for ECDH key derivation.EVP_PKEY_CTX_get_ecdh_kdf_outlen()— gets the key derivation function output length for ctx used for ECDH key derivation.EVP_PKEY_CTX_set0_ecdh_kdf_ukm()— 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.EVP_PKEY_CTX_get0_ecdh_kdf_ukm()— 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 ⭐
EVP_PKEY_CTX_set1_id(), EVP_PKEY_CTX_get1_id() and EVP_PKEY_CTX_get1_id_len() 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. EVP_PKEY_CTX_get1_id_len() 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(). EVP_PKEY_CTX_get1_id() 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(). allocate first, then ask, bestie 🎀
EVP_PKEY_CTX_set_kem_op() sets the KEM operation to run. This can be set after EVP_PKEY_encapsulate_init() or EVP_PKEY_decapsulate_init() to select the kem operation. For the key types that support encapsulation and don't have the default operation, e.g. RSA, this function must be called before EVP_PKEY_encapsulate() or EVP_PKEY_decapsulate(). 🚨
The supported parameters for the built-in algorithms are documented in EVP_KEM-RSA(7), EVP_KEM-EC(7), EVP_KEM-X25519(7), EVP_KEM-X448(7), and EVP_KEM-ML-KEM(7). go read those next, homework era 📚
🫶 RETURN VALUES 🫶
All other functions 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. so if you see -2, it's not you, it's the algorithm 💀
👀 SEE ALSO 👀
EVP_PKEY_CTX_set_params(3), 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) EVP_PKEY_encapsulate(3) EVP_PKEY_decapsulate(3)
✨ HISTORY ✨
okay so bestie, here's the timeline of how all these lil guys showed up 💖
EVP_PKEY_CTX_get_rsa_oaep_md_name(),EVP_PKEY_CTX_get_rsa_mgf1_md_name(),EVP_PKEY_CTX_set_rsa_mgf1_md_name(),EVP_PKEY_CTX_set_rsa_oaep_md_name(),EVP_PKEY_CTX_set_dsa_paramgen_md_props(),EVP_PKEY_CTX_set_dsa_paramgen_gindex(),EVP_PKEY_CTX_set_dsa_paramgen_type(),EVP_PKEY_CTX_set_dsa_paramgen_seed(),EVP_PKEY_CTX_set_group_name()andEVP_PKEY_CTX_get_group_name()all got added in OpenSSL 3.0 🌈✨- The
EVP_PKEY_CTX_set1_id(),EVP_PKEY_CTX_get1_id()andEVP_PKEY_CTX_get1_id_len()macros? those entered the chat in 1.1.1 🫶 and all the other functions were added in OpenSSL 1.0.0 💅 - ngl there was a lil glow-up moment: in OpenSSL 1.1.1 and below these functions were mostly macros. From OpenSSL 3.0 onward, they are all functions 🔥 like, character development fr fr
- and bestie, we gotta hold a tiny funeral for these ones 😭
EVP_PKEY_CTX_set_rsa_keygen_pubexp(),EVP_PKEY_CTX_get0_dh_kdf_ukm(), andEVP_PKEY_CTX_get0_ecdh_kdf_ukm()were deprecated in OpenSSL 3.0 💀 rest in peace kings
👑 COPYRIGHT 👑
Copyright 2006-2025 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>.
and that's a wrap on this whole entire manpage, bestie!! 🦋 this lil trip through the docs came from the 4.0.3 release, dated 2026-09-29, and you read it via EVP_PKEY_CTX_CTRL(3SSL) ✨ go forth and call those macros—sorry, functions 💅 slay 💖🌸
📦 where this page comes from
- ubuntu stonking: libssl-doc 4.0.3-1ubuntu1 · Apache-2.0
- 💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash on : a language model's rewrite of the original, under its terms