EVP_OPENINIT(3) | Library Functions Manual | EVP_OPENINIT(3)

# NAME

`EVP_OpenInit`, `EVP_OpenUpdate`, `EVP_OpenFinal` — EVP envelope decryption

# SYNOPSIS

library “libcrypto”
`#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);

# DESCRIPTION

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(3) and EVP_DecryptFinal(3) routines.

It is possible to call `EVP_OpenInit`() twice in the same way as EVP_DecryptInit(3). 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_OpenUpdate`() is implemented as a macro.

# RETURN VALUES

`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.

# SEE ALSO

evp(3), EVP_EncryptInit(3), EVP_SealInit(3)

# HISTORY

`EVP_OpenInit`(), `EVP_OpenUpdate`(), and `EVP_OpenFinal`() first appeared in SSLeay 0.5.1 and have been available since OpenBSD 2.4.

June 8, 2025 | Debian