EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope
unsigned char **ek,
unsigned char *iv,
int npubk ); int EVP_SealUpdate(
unsigned char *out,
unsigned char *in,
int inl ); int EVP_SealFinal(
unsigned char *out,
int *outl );
The EVP envelope routines are a high level interface to
envelope encryption. They generate a random key and then
envelope it by using public key encryption. Data can then
be encrypted using this key.
The EVP_SealInit() function initializes a cipher context
ctx for encryption with cipher type using a random secret
key and IV supplied in the iv parameter. The 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. The 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. The pubk
is an array of npubk public keys.
The EVP_SealUpdate() and EVP_SealFinal() functions have
the same properties as the EVP_EncryptUpdate() and
EVP_EncryptFinal() functions, as documented on the
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.
The EVP_SealInit() function returns 0 on error or npubk if
The EVP_SealUpdate() and EVP_SealFinal() functions return
1 for success and 0 for failure.
Functions: evp(3), rand_ssl(3), EVP_EncryptInit(3),
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