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✏️ Editing: EVP_PKEY_meth_set_verify_recover.3

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.\" ========================================================================
.\"
.IX Title "EVP_PKEY_METH_NEW 3"
.TH EVP_PKEY_METH_NEW 3 "2023-09-11" "1.1.1w" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
EVP_PKEY_meth_new, EVP_PKEY_meth_free, EVP_PKEY_meth_copy, EVP_PKEY_meth_find, EVP_PKEY_meth_add0, EVP_PKEY_METHOD, EVP_PKEY_meth_set_init, EVP_PKEY_meth_set_copy, EVP_PKEY_meth_set_cleanup, EVP_PKEY_meth_set_paramgen, EVP_PKEY_meth_set_keygen, EVP_PKEY_meth_set_sign, EVP_PKEY_meth_set_verify, EVP_PKEY_meth_set_verify_recover, EVP_PKEY_meth_set_signctx, EVP_PKEY_meth_set_verifyctx, EVP_PKEY_meth_set_encrypt, EVP_PKEY_meth_set_decrypt, EVP_PKEY_meth_set_derive, EVP_PKEY_meth_set_ctrl, EVP_PKEY_meth_set_digestsign, EVP_PKEY_meth_set_digestverify, EVP_PKEY_meth_set_check, EVP_PKEY_meth_set_public_check, EVP_PKEY_meth_set_param_check, EVP_PKEY_meth_set_digest_custom, EVP_PKEY_meth_get_init, EVP_PKEY_meth_get_copy, EVP_PKEY_meth_get_cleanup, EVP_PKEY_meth_get_paramgen, EVP_PKEY_meth_get_keygen, EVP_PKEY_meth_get_sign, EVP_PKEY_meth_get_verify, EVP_PKEY_meth_get_verify_recover, EVP_PKEY_meth_get_signctx, EVP_PKEY_meth_get_verifyctx, EVP_PKEY_meth_get_encrypt, EVP_PKEY_meth_get_decrypt, EVP_PKEY_meth_get_derive, EVP_PKEY_meth_get_ctrl, EVP_PKEY_meth_get_digestsign, EVP_PKEY_meth_get_digestverify, EVP_PKEY_meth_get_check, EVP_PKEY_meth_get_public_check, EVP_PKEY_meth_get_param_check, EVP_PKEY_meth_get_digest_custom, EVP_PKEY_meth_remove \&\- manipulating EVP_PKEY_METHOD structure
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\& #include <openssl/evp.h>
\&
\& typedef struct evp_pkey_method_st EVP_PKEY_METHOD;
\&
\& EVP_PKEY_METHOD *EVP_PKEY_meth_new(int id, int flags);
\& void EVP_PKEY_meth_free(EVP_PKEY_METHOD *pmeth);
\& void EVP_PKEY_meth_copy(EVP_PKEY_METHOD *dst, const EVP_PKEY_METHOD *src);
\& const EVP_PKEY_METHOD *EVP_PKEY_meth_find(int type);
\& int EVP_PKEY_meth_add0(const EVP_PKEY_METHOD *pmeth);
\& int EVP_PKEY_meth_remove(const EVP_PKEY_METHOD *pmeth);
\&
\& void EVP_PKEY_meth_set_init(EVP_PKEY_METHOD *pmeth,
\&                             int (*init) (EVP_PKEY_CTX *ctx));
\& void EVP_PKEY_meth_set_copy(EVP_PKEY_METHOD *pmeth,
\&                             int (*copy) (EVP_PKEY_CTX *dst,
\&                                          EVP_PKEY_CTX *src));
\& void EVP_PKEY_meth_set_cleanup(EVP_PKEY_METHOD *pmeth,
\&                                void (*cleanup) (EVP_PKEY_CTX *ctx));
\& void EVP_PKEY_meth_set_paramgen(EVP_PKEY_METHOD *pmeth,
\&                                 int (*paramgen_init) (EVP_PKEY_CTX *ctx),
\&                                 int (*paramgen) (EVP_PKEY_CTX *ctx,
\&                                                  EVP_PKEY *pkey));
\& void EVP_PKEY_meth_set_keygen(EVP_PKEY_METHOD *pmeth,
\&                               int (*keygen_init) (EVP_PKEY_CTX *ctx),
\&                               int (*keygen) (EVP_PKEY_CTX *ctx,
\&                                              EVP_PKEY *pkey));
\& void EVP_PKEY_meth_set_sign(EVP_PKEY_METHOD *pmeth,
\&                             int (*sign_init) (EVP_PKEY_CTX *ctx),
\&                             int (*sign) (EVP_PKEY_CTX *ctx,
\&                                          unsigned char *sig, size_t *siglen,
\&                                          const unsigned char *tbs,
\&                                          size_t tbslen));
\& void EVP_PKEY_meth_set_verify(EVP_PKEY_METHOD *pmeth,
\&                               int (*verify_init) (EVP_PKEY_CTX *ctx),
\&                               int (*verify) (EVP_PKEY_CTX *ctx,
\&                                              const unsigned char *sig,
\&                                              size_t siglen,
\&                                              const unsigned char *tbs,
\&                                              size_t tbslen));
\& void EVP_PKEY_meth_set_verify_recover(EVP_PKEY_METHOD *pmeth,
\&                                       int (*verify_recover_init) (EVP_PKEY_CTX
\&                                                                   *ctx),
\&                                       int (*verify_recover) (EVP_PKEY_CTX
\&                                                              *ctx,
\&                                                              unsigned char
\&                                                              *sig,
\&                                                              size_t *siglen,
\&                                                              const unsigned
\&                                                              char *tbs,
\&                                                              size_t tbslen));
\& void EVP_PKEY_meth_set_signctx(EVP_PKEY_METHOD *pmeth,
\&                                int (*signctx_init) (EVP_PKEY_CTX *ctx,
\&                                                     EVP_MD_CTX *mctx),
\&                                int (*signctx) (EVP_PKEY_CTX *ctx,
\&                                                unsigned char *sig,
\&                                                size_t *siglen,
\&                                                EVP_MD_CTX *mctx));
\& void EVP_PKEY_meth_set_verifyctx(EVP_PKEY_METHOD *pmeth,
\&                                  int (*verifyctx_init) (EVP_PKEY_CTX *ctx,
\&                                                         EVP_MD_CTX *mctx),
\&                                  int (*verifyctx) (EVP_PKEY_CTX *ctx,
\&                                                    const unsigned char *sig,
\&                                                    int siglen,
\&                                                    EVP_MD_CTX *mctx));
\& void EVP_PKEY_meth_set_encrypt(EVP_PKEY_METHOD *pmeth,
\&                                int (*encrypt_init) (EVP_PKEY_CTX *ctx),
\&                                int (*encryptfn) (EVP_PKEY_CTX *ctx,
\&                                                  unsigned char *out,
\&                                                  size_t *outlen,
\&                                                  const unsigned char *in,
\&                                                  size_t inlen));
\& void EVP_PKEY_meth_set_decrypt(EVP_PKEY_METHOD *pmeth,
\&                                int (*decrypt_init) (EVP_PKEY_CTX *ctx),
\&                                int (*decrypt) (EVP_PKEY_CTX *ctx,
\&                                                unsigned char *out,
\&                                                size_t *outlen,
\&                                                const unsigned char *in,
\&                                                size_t inlen));
\& void EVP_PKEY_meth_set_derive(EVP_PKEY_METHOD *pmeth,
\&                               int (*derive_init) (EVP_PKEY_CTX *ctx),
\&                               int (*derive) (EVP_PKEY_CTX *ctx,
\&                                              unsigned char *key,
\&                                              size_t *keylen));
\& void EVP_PKEY_meth_set_ctrl(EVP_PKEY_METHOD *pmeth,
\&                             int (*ctrl) (EVP_PKEY_CTX *ctx, int type, int p1,
\&                                          void *p2),
\&                             int (*ctrl_str) (EVP_PKEY_CTX *ctx,
\&                                              const char *type,
\&                                              const char *value));
\& void EVP_PKEY_meth_set_digestsign(EVP_PKEY_METHOD *pmeth,
\&                                   int (*digestsign) (EVP_MD_CTX *ctx,
\&                                                      unsigned char *sig,
\&                                                      size_t *siglen,
\&                                                      const unsigned char *tbs,
\&                                                      size_t tbslen));
\& void EVP_PKEY_meth_set_digestverify(EVP_PKEY_METHOD *pmeth,
\&                                     int (*digestverify) (EVP_MD_CTX *ctx,
\&                                                          const unsigned char *sig,
\&                                                          size_t siglen,
\&                                                          const unsigned char *tbs,
\&                                                          size_t tbslen));
\& void EVP_PKEY_meth_set_check(EVP_PKEY_METHOD *pmeth,
\&                              int (*check) (EVP_PKEY *pkey));
\& void EVP_PKEY_meth_set_public_check(EVP_PKEY_METHOD *pmeth,
\&                                     int (*check) (EVP_PKEY *pkey));
\& void EVP_PKEY_meth_set_param_check(EVP_PKEY_METHOD *pmeth,
\&                                    int (*check) (EVP_PKEY *pkey));
\& void EVP_PKEY_meth_set_digest_custom(EVP_PKEY_METHOD *pmeth,
\&                                     int (*digest_custom) (EVP_PKEY_CTX *ctx,
\&                                                           EVP_MD_CTX *mctx));
\&
\& void EVP_PKEY_meth_get_init(const EVP_PKEY_METHOD *pmeth,
\&                             int (**pinit) (EVP_PKEY_CTX *ctx));
\& void EVP_PKEY_meth_get_copy(const EVP_PKEY_METHOD *pmeth,
\&                             int (**pcopy) (EVP_PKEY_CTX *dst,
\&                                            EVP_PKEY_CTX *src));
\& void EVP_PKEY_meth_get_cleanup(const EVP_PKEY_METHOD *pmeth,
\&                                void (**pcleanup) (EVP_PKEY_CTX *ctx));
\& void EVP_PKEY_meth_get_paramgen(const EVP_PKEY_METHOD *pmeth,
\&                                 int (**pparamgen_init) (EVP_PKEY_CTX *ctx),
\&                                 int (**pparamgen) (EVP_PKEY_CTX *ctx,
\&                                                    EVP_PKEY *pkey));
\& void EVP_PKEY_meth_get_keygen(const EVP_PKEY_METHOD *pmeth,
\&                               int (**pkeygen_init) (EVP_PKEY_CTX *ctx),
\&                               int (**pkeygen) (EVP_PKEY_CTX *ctx,
\&                                                EVP_PKEY *pkey));
\& void EVP_PKEY_meth_get_sign(const EVP_PKEY_METHOD *pmeth,
\&                             int (**psign_init) (EVP_PKEY_CTX *ctx),
\&                             int (**psign) (EVP_PKEY_CTX *ctx,
\&                                            unsigned char *sig, size_t *siglen,
\&                                            const unsigned char *tbs,
\&                                            size_t tbslen));
\& void EVP_PKEY_meth_get_verify(const EVP_PKEY_METHOD *pmeth,
\&                               int (**pverify_init) (EVP_PKEY_CTX *ctx),
\&                               int (**pverify) (EVP_PKEY_CTX *ctx,
\&                                                const unsigned char *sig,
\&                                                size_t siglen,
\&                                                const unsigned char *tbs,
\&                                                size_t tbslen));
\& void EVP_PKEY_meth_get_verify_recover(const EVP_PKEY_METHOD *pmeth,
\&                                       int (**pverify_recover_init) (EVP_PKEY_CTX
\&                                                                     *ctx),
\&                                       int (**pverify_recover) (EVP_PKEY_CTX
\&                                                                *ctx,
\&                                                                unsigned char
\&                                                                *sig,
\&                                                                size_t *siglen,
\&                                                                const unsigned
\&                                                                char *tbs,
\&                                                                size_t tbslen));
\& void EVP_PKEY_meth_get_signctx(const EVP_PKEY_METHOD *pmeth,
\&                                int (**psignctx_init) (EVP_PKEY_CTX *ctx,
\&                                                       EVP_MD_CTX *mctx),
\&                                int (**psignctx) (EVP_PKEY_CTX *ctx,
\&                                                  unsigned char *sig,
\&                                                  size_t *siglen,
\&                                                  EVP_MD_CTX *mctx));
\& void EVP_PKEY_meth_get_verifyctx(const EVP_PKEY_METHOD *pmeth,
\&                                  int (**pverifyctx_init) (EVP_PKEY_CTX *ctx,
\&                                                           EVP_MD_CTX *mctx),
\&                                  int (**pverifyctx) (EVP_PKEY_CTX *ctx,
\&                                                      const unsigned char *sig,
\&                                                      int siglen,
\&                                                      EVP_MD_CTX *mctx));
\& void EVP_PKEY_meth_get_encrypt(const EVP_PKEY_METHOD *pmeth,
\&                                int (**pencrypt_init) (EVP_PKEY_CTX *ctx),
\&                                int (**pencryptfn) (EVP_PKEY_CTX *ctx,
\&                                                    unsigned char *out,
\&                                                    size_t *outlen,
\&                                                    const unsigned char *in,
\&                                                    size_t inlen));
\& void EVP_PKEY_meth_get_decrypt(const EVP_PKEY_METHOD *pmeth,
\&                                int (**pdecrypt_init) (EVP_PKEY_CTX *ctx),
\&                                int (**pdecrypt) (EVP_PKEY_CTX *ctx,
\&                                                  unsigned char *out,
\&                                                  size_t *outlen,
\&                                                  const unsigned char *in,
\&                                                  size_t inlen));
\& void EVP_PKEY_meth_get_derive(const EVP_PKEY_METHOD *pmeth,
\&                               int (**pderive_init) (EVP_PKEY_CTX *ctx),
\&                               int (**pderive) (EVP_PKEY_CTX *ctx,
\&                                                unsigned char *key,
\&                                                size_t *keylen));
\& void EVP_PKEY_meth_get_ctrl(const EVP_PKEY_METHOD *pmeth,
\&                             int (**pctrl) (EVP_PKEY_CTX *ctx, int type, int p1,
\&                                            void *p2),
\&                             int (**pctrl_str) (EVP_PKEY_CTX *ctx,
\&                                                const char *type,
\&                                                const char *value));
\& void EVP_PKEY_meth_get_digestsign(EVP_PKEY_METHOD *pmeth,
\&                                   int (**digestsign) (EVP_MD_CTX *ctx,
\&                                                       unsigned char *sig,
\&                                                       size_t *siglen,
\&                                                       const unsigned char *tbs,
\&                                                       size_t tbslen));
\& void EVP_PKEY_meth_get_digestverify(EVP_PKEY_METHOD *pmeth,
\&                                     int (**digestverify) (EVP_MD_CTX *ctx,
\&                                                           const unsigned char *sig,
\&                                                           size_t siglen,
\&                                                           const unsigned char *tbs,
\&                                                           size_t tbslen));
\& void EVP_PKEY_meth_get_check(const EVP_PKEY_METHOD *pmeth,
\&                              int (**pcheck) (EVP_PKEY *pkey));
\& void EVP_PKEY_meth_get_public_check(const EVP_PKEY_METHOD *pmeth,
\&                                     int (**pcheck) (EVP_PKEY *pkey));
\& void EVP_PKEY_meth_get_param_check(const EVP_PKEY_METHOD *pmeth,
\&                                    int (**pcheck) (EVP_PKEY *pkey));
\& void EVP_PKEY_meth_get_digest_custom(EVP_PKEY_METHOD *pmeth,
\&                                     int (**pdigest_custom) (EVP_PKEY_CTX *ctx,
\&                                                             EVP_MD_CTX *mctx));
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
\&\fB\s-1EVP_PKEY_METHOD\s0\fR is a structure which holds a set of methods for a
specific public key cryptographic algorithm. Those methods are usually
used to perform different jobs, such as generating a key, signing or
verifying, encrypting or decrypting, etc.
.PP
There are two places where the \fB\s-1EVP_PKEY_METHOD\s0\fR objects are stored: one
is a built-in static array representing the standard methods for different
algorithms, and the other one is a stack of user-defined application-specific
methods, which can be manipulated by using \fBEVP_PKEY_meth_add0\fR\|(3).
.PP
The \fB\s-1EVP_PKEY_METHOD\s0\fR objects are usually referenced by \fB\s-1EVP_PKEY_CTX\s0\fR
objects.
.SS "Methods"
.IX Subsection "Methods"
The methods are the underlying implementations of a particular public key
algorithm present by the \fB\s-1EVP_PKEY_CTX\s0\fR object.
.PP
.Vb 3
\& int (*init) (EVP_PKEY_CTX *ctx);
\& int (*copy) (EVP_PKEY_CTX *dst, EVP_PKEY_CTX *src);
\& void (*cleanup) (EVP_PKEY_CTX *ctx);
.Ve
.PP
The \fBinit()\fR method is called to initialize algorithm-specific data when a new
\&\fB\s-1EVP_PKEY_CTX\s0\fR is created. As opposed to \fBinit()\fR, the \fBcleanup()\fR method is called
when an \fB\s-1EVP_PKEY_CTX\s0\fR is freed. The \fBcopy()\fR method is called when an \fB\s-1EVP_PKEY_CTX\s0\fR
is being duplicated. Refer to \fBEVP_PKEY_CTX_new\fR\|(3), \fBEVP_PKEY_CTX_new_id\fR\|(3),
\&\fBEVP_PKEY_CTX_free\fR\|(3) and \fBEVP_PKEY_CTX_dup\fR\|(3).
.PP
.Vb 2
\& int (*paramgen_init) (EVP_PKEY_CTX *ctx);
\& int (*paramgen) (EVP_PKEY_CTX *ctx, EVP_PKEY *pkey);
.Ve
.PP
The \fBparamgen_init()\fR and \fBparamgen()\fR methods deal with key parameter generation.
They are called by \fBEVP_PKEY_paramgen_init\fR\|(3) and \fBEVP_PKEY_paramgen\fR\|(3) to
handle the parameter generation process.
.PP
.Vb 2
\& int (*keygen_init) (EVP_PKEY_CTX *ctx);
\& int (*keygen) (EVP_PKEY_CTX *ctx, EVP_PKEY *pkey);
.Ve
.PP
The \fBkeygen_init()\fR and \fBkeygen()\fR methods are used to generate the actual key for
the specified algorithm. They are called by \fBEVP_PKEY_keygen_init\fR\|(3) and
\&\fBEVP_PKEY_keygen\fR\|(3).
.PP
.Vb 3
\& int (*sign_init) (EVP_PKEY_CTX *ctx);
\& int (*sign) (EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen,
\&              const unsigned char *tbs, size_t tbslen);
.Ve
.PP
The \fBsign_init()\fR and \fBsign()\fR methods are used to generate the signature of a
piece of data using a private key. They are called by \fBEVP_PKEY_sign_init\fR\|(3)
and \fBEVP_PKEY_sign\fR\|(3).
.PP
.Vb 4
\& int (*verify_init) (EVP_PKEY_CTX *ctx);
\& int (*verify) (EVP_PKEY_CTX *ctx,
\&                const unsigned char *sig, size_t siglen,
\&                const unsigned char *tbs, size_t tbslen);
.Ve
.PP
The \fBverify_init()\fR and \fBverify()\fR methods are used to verify whether a signature is
valid. They are called by \fBEVP_PKEY_verify_init\fR\|(3) and \fBEVP_PKEY_verify\fR\|(3).
.PP
.Vb 4
\& int (*verify_recover_init) (EVP_PKEY_CTX *ctx);
\& int (*verify_recover) (EVP_PKEY_CTX *ctx,
\&                        unsigned char *rout, size_t *routlen,
\&                        const unsigned char *sig, size_t siglen);
.Ve
.PP
The \fBverify_recover_init()\fR and \fBverify_recover()\fR methods are used to verify a
signature and then recover the digest from the signature (for instance, a
signature that was generated by \s-1RSA\s0 signing algorithm). They are called by
\&\fBEVP_PKEY_verify_recover_init\fR\|(3) and \fBEVP_PKEY_verify_recover\fR\|(3).
.PP
.Vb 3
\& int (*signctx_init) (EVP_PKEY_CTX *ctx, EVP_MD_CTX *mctx);
\& int (*signctx) (EVP_PKEY_CTX *ctx, unsigned char *sig, size_t *siglen,
\&                 EVP_MD_CTX *mctx);
.Ve
.PP
The \fBsignctx_init()\fR and \fBsignctx()\fR methods are used to sign a digest present by
a \fB\s-1EVP_MD_CTX\s0\fR object. They are called by the EVP_DigestSign functions. See
\&\fBEVP_DigestSignInit\fR\|(3) for details.
.PP
.Vb 3
\& int (*verifyctx_init) (EVP_PKEY_CTX *ctx, EVP_MD_CTX *mctx);
\& int (*verifyctx) (EVP_PKEY_CTX *ctx, const unsigned char *sig, int siglen,
\&                   EVP_MD_CTX *mctx);
.Ve
.PP
The \fBverifyctx_init()\fR and \fBverifyctx()\fR methods are used to verify a signature
against the data in a \fB\s-1EVP_MD_CTX\s0\fR object. They are called by the various
EVP_DigestVerify functions. See \fBEVP_DigestVerifyInit\fR\|(3) for details.
.PP
.Vb 3
\& int (*encrypt_init) (EVP_PKEY_CTX *ctx);
\& int (*encrypt) (EVP_PKEY_CTX *ctx, unsigned char *out, size_t *outlen,
\&                 const unsigned char *in, size_t inlen);
.Ve
.PP
The \fBencrypt_init()\fR and \fBencrypt()\fR methods are used to encrypt a piece of data.
They are called by \fBEVP_PKEY_encrypt_init\fR\|(3) and \fBEVP_PKEY_encrypt\fR\|(3).
.PP
.Vb 3
\& int (*decrypt_init) (EVP_PKEY_CTX *ctx);
\& int (*decrypt) (EVP_PKEY_CTX *ctx, unsigned char *out, size_t *outlen,
\&                 const unsigned char *in, size_t inlen);
.Ve
.PP
The \fBdecrypt_init()\fR and \fBdecrypt()\fR methods are used to decrypt a piece of data.
They are called by \fBEVP_PKEY_decrypt_init\fR\|(3) and \fBEVP_PKEY_decrypt\fR\|(3).
.PP
.Vb 2
\& int (*derive_init) (EVP_PKEY_CTX *ctx);
\& int (*derive) (EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);
.Ve
.PP
The \fBderive_init()\fR and \fBderive()\fR methods are used to derive the shared secret
from a public key algorithm (for instance, the \s-1DH\s0 algorithm). They are called by
\&\fBEVP_PKEY_derive_init\fR\|(3) and \fBEVP_PKEY_derive\fR\|(3).
.PP
.Vb 2
\& int (*ctrl) (EVP_PKEY_CTX *ctx, int type, int p1, void *p2);
\& int (*ctrl_str) (EVP_PKEY_CTX *ctx, const char *type, const char *value);
.Ve
.PP
The \fBctrl()\fR and \fBctrl_str()\fR methods are used to adjust algorithm-specific
settings. See \fBEVP_PKEY_CTX_ctrl\fR\|(3) and related functions for details.
.PP
.Vb 5
\& int (*digestsign) (EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen,
\&                    const unsigned char *tbs, size_t tbslen);
\& int (*digestverify) (EVP_MD_CTX *ctx, const unsigned char *sig,
\&                      size_t siglen, const unsigned char *tbs,
\&                      size_t tbslen);
.Ve
.PP
The \fBdigestsign()\fR and \fBdigestverify()\fR methods are used to generate or verify
a signature in a one-shot mode. They could be called by \fBEVP_DigestSign\fR\|(3)
and \fBEVP_DigestVerify\fR\|(3).
.PP
.Vb 3
\& int (*check) (EVP_PKEY *pkey);
\& int (*public_check) (EVP_PKEY *pkey);
\& int (*param_check) (EVP_PKEY *pkey);
.Ve
.PP
The \fBcheck()\fR, \fBpublic_check()\fR and \fBparam_check()\fR methods are used to validate a
key-pair, the public component and parameters respectively for a given \fBpkey\fR.
They could be called by \fBEVP_PKEY_check\fR\|(3), \fBEVP_PKEY_public_check\fR\|(3) and
\&\fBEVP_PKEY_param_check\fR\|(3) respectively.
.PP
.Vb 1
\& int (*digest_custom) (EVP_PKEY_CTX *ctx, EVP_MD_CTX *mctx);
.Ve
.PP
The \fBdigest_custom()\fR method is used to generate customized digest content before
the real message is passed to functions like \fBEVP_DigestSignUpdate\fR\|(3) or
\&\fBEVP_DigestVerifyInit\fR\|(3). This is usually required by some public key
signature algorithms like \s-1SM2\s0 which requires a hashed prefix to the message to
be signed. The \fBdigest_custom()\fR function will be called by \fBEVP_DigestSignInit\fR\|(3)
and \fBEVP_DigestVerifyInit\fR\|(3).
.SS "Functions"
.IX Subsection "Functions"
\&\fBEVP_PKEY_meth_new()\fR creates and returns a new \fB\s-1EVP_PKEY_METHOD\s0\fR object,
and associates the given \fBid\fR and \fBflags\fR. The following flags are
supported:
.PP
.Vb 2
\& EVP_PKEY_FLAG_AUTOARGLEN
\& EVP_PKEY_FLAG_SIGCTX_CUSTOM
.Ve
.PP
If an \fB\s-1EVP_PKEY_METHOD\s0\fR is set with the \fB\s-1EVP_PKEY_FLAG_AUTOARGLEN\s0\fR flag, the
maximum size of the output buffer will be automatically calculated or checked
in corresponding \s-1EVP\s0 methods by the \s-1EVP\s0 framework. Thus the implementations of
these methods don't need to care about handling the case of returning output
buffer size by themselves. For details on the output buffer size, refer to
\&\fBEVP_PKEY_sign\fR\|(3).
.PP
The \fB\s-1EVP_PKEY_FLAG_SIGCTX_CUSTOM\s0\fR is used to indicate the \fBsignctx()\fR method
of an \fB\s-1EVP_PKEY_METHOD\s0\fR is always called by the \s-1EVP\s0 framework while doing a
digest signing operation by calling \fBEVP_DigestSignFinal\fR\|(3).
.PP
\&\fBEVP_PKEY_meth_free()\fR frees an existing \fB\s-1EVP_PKEY_METHOD\s0\fR pointed by
\&\fBpmeth\fR.
.PP
\&\fBEVP_PKEY_meth_copy()\fR copies an \fB\s-1EVP_PKEY_METHOD\s0\fR object from \fBsrc\fR
to \fBdst\fR.
.PP
\&\fBEVP_PKEY_meth_find()\fR finds an \fB\s-1EVP_PKEY_METHOD\s0\fR object with the \fBid\fR.
This function first searches through the user-defined method objects and
then the built-in objects.
.PP
\&\fBEVP_PKEY_meth_add0()\fR adds \fBpmeth\fR to the user defined stack of methods.
.PP
\&\fBEVP_PKEY_meth_remove()\fR removes an \fB\s-1EVP_PKEY_METHOD\s0\fR object added by
\&\fBEVP_PKEY_meth_add0()\fR.
.PP
The EVP_PKEY_meth_set functions set the corresponding fields of
\&\fB\s-1EVP_PKEY_METHOD\s0\fR structure with the arguments passed.
.PP
The EVP_PKEY_meth_get functions get the corresponding fields of
\&\fB\s-1EVP_PKEY_METHOD\s0\fR structure to the arguments provided.
.SH "RETURN VALUES"
.IX Header "RETURN VALUES"
\&\fBEVP_PKEY_meth_new()\fR returns a pointer to a new \fB\s-1EVP_PKEY_METHOD\s0\fR
object or returns \s-1NULL\s0 on error.
.PP
\&\fBEVP_PKEY_meth_free()\fR and \fBEVP_PKEY_meth_copy()\fR do not return values.
.PP
\&\fBEVP_PKEY_meth_find()\fR returns a pointer to the found \fB\s-1EVP_PKEY_METHOD\s0\fR
object or returns \s-1NULL\s0 if not found.
.PP
\&\fBEVP_PKEY_meth_add0()\fR returns 1 if method is added successfully or 0
if an error occurred.
.PP
\&\fBEVP_PKEY_meth_remove()\fR returns 1 if method is removed successfully or
0 if an error occurred.
.PP
All EVP_PKEY_meth_set and EVP_PKEY_meth_get functions have no return
values. For the 'get' functions, function pointers are returned by
arguments.
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2017\-2019 The OpenSSL Project Authors. All Rights Reserved.
.PP
Licensed under the OpenSSL license (the \*(L"License\*(R").  You may not use
this file except in compliance with the License.  You can obtain a copy
in the file \s-1LICENSE\s0 in the source distribution or at
<https://www.openssl.org/source/license.html>.

MR SKB