EVP_SealInit(3) OpenSSL EVP_SealInit(3)
NAME
EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption
SYNOPSIS
#include <openssl/evp.h>
int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
unsigned char **ek, int *ekl, unsigned char *iv,
EVP_PKEY **pubk, int npubk);
int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl, unsigned char *in, int inl);
int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
int *outl);
DESCRIPTION
The EVP envelope routines are a high level interface to envelope encryption. They generate a random
key and IV (if required) then "envelope" it by using public key encryption. Data can then be
encrypted using this key.
EVP_SealInit() initializes a cipher context ctx for encryption with cipher type using a random secret
key and IV. type is normally supplied by a function such as EVP_des_cbc(). The secret key is
encrypted using one or more public keys, this allows the same encrypted data to be decrypted using
any of the corresponding private keys. ek is an array of buffers where the public key encrypted
secret key will be written, each buffer must contain enough room for the corresponding encrypted key:
that is ek[i] must have room for EVP_PKEY_size(pubk[i]) bytes. The actual size of each encrypted
secret key is written to the array ekl. pubk is an array of npubk public keys.
The iv parameter is a buffer where the generated IV is written to. It must contain enough room for
the corresponding cipher's IV, as determined by (for example) EVP_CIPHER_iv_length(type).
If the cipher does not require an IV then the iv parameter is ignored and can be NULL.
EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties as the EVP_EncryptUpdate() and
EVP_EncryptFinal() routines, as documented on the EVP_EncryptInit(3) manual page.
RETURN VALUES
EVP_SealInit() returns 0 on error or npubk if successful.
EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for failure.
NOTES
Because a random secret key is generated the random number generator must be seeded before calling
EVP_SealInit().
The public key must be RSA because it is the only OpenSSL public key algorithm that supports key
transport.
Envelope encryption is the usual method of using public key encryption on large amounts of data, this
is because public key encryption is slow but symmetric encryption is fast. So symmetric encryption is
used for bulk encryption and the small random symmetric key used is transferred using public key
encryption.
It is possible to call EVP_SealInit() twice in the same way as EVP_EncryptInit(). The first call
should have npubk set to 0 and (after setting any cipher parameters) it should be called again with
type set to NULL.
SEE ALSO
evp(3), rand(3), EVP_EncryptInit(3), EVP_OpenInit(3)
HISTORY
EVP_SealFinal() did not return a value before OpenSSL 0.9.7.
0.9.7l 2005-03-29 EVP_SealInit(3)
|