EVP_OpenInit, EVP_OpenUpdate, EVP_OpenFinal - EVP envelope decryption

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       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>.

3.5.0                                              2025-06-04                                 EVP_OPENINIT(3SSL)

       The EVP envelope routines are a high-level interface to envelope decryption. They decrypt a public key
       encrypted symmetric key and then decrypt data using it.

       EVP_OpenInit() initializes a cipher context ctx for decryption with cipher type. It decrypts the
       encrypted symmetric key of length ekl bytes passed in the ek parameter using the private key priv.  The
       IV is supplied in the iv parameter.

       EVP_OpenUpdate() and EVP_OpenFinal() have exactly the same properties as the EVP_DecryptUpdate() and
       EVP_DecryptFinal() routines, as documented on the EVP_EncryptInit(3) manual page.

       EVP_OpenInit, EVP_OpenUpdate, EVP_OpenFinal - EVP envelope decryption

       It is possible to call EVP_OpenInit() twice in the same way as EVP_DecryptInit(). The first call should
       have priv set to NULL and (after setting any cipher parameters) it should be called again with type set
       to NULL.

       If the cipher passed in the type parameter is a variable length cipher then the key length will be set to
       the value of the recovered key length. If the cipher is a fixed length cipher then the recovered key
       length must match the fixed cipher length.

EVP_OpenInit() returns 0 on error or a non zero integer (actually the recovered secret key size) if
       successful.

       EVP_OpenUpdate() returns 1 for success or 0 for failure.

       EVP_OpenFinal() returns 0 if the decrypt failed or 1 for success.

evp(7), RAND_bytes(3), EVP_EncryptInit(3), EVP_SealInit(3)

        #include <openssl/evp.h>

        int EVP_OpenInit(EVP_CIPHER_CTX *ctx, EVP_CIPHER *type, unsigned char *ek,
                         int ekl, unsigned char *iv, EVP_PKEY *priv);
        int EVP_OpenUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
                           int *outl, unsigned char *in, int inl);
        int EVP_OpenFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);