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_aes_256_cbc(3); see
EVP_EncryptInit(3) for details. 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(3) and
EVP_EncryptFinal(3) routines.
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(3). 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.
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.
SEE ALSO
HISTORY
EVP_SealInit(),
EVP_SealUpdate(), and
EVP_SealFinal() first appeared in SSLeay 0.5.1 and
have been available since OpenBSD 2.4.
EVP_SealFinal() did not return a value
before OpenSSL 0.9.7.