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 encryp-
tion 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 writ-
ten 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 VALUESEVP_SealInit() returns 0 on error or npubk if successful.
EVP_SealUpdate() and EVP_SealFinal() return 1 for success
and 0 for failure.
MirOS BSD #10-current 2005-04-29 1
EVP_SEALINIT(3) OpenSSL EVP_SEALINIT(3)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 ALSOevp(3), rand(3), EVP_EncryptInit(3), EVP_OpenInit(3)HISTORYEVP_SealFinal() did not return a value before OpenSSL 0.9.7.
MirOS BSD #10-current 2005-04-29 2
