EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope
int EVP_SealInit(EVP_CIPHER_CTX *ctx, 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,
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.
EVP_SealInit() initializes a cipher context ctx for
encryption with cipher type using a random secret key and
IV supplied in the iv parameter. 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.
EVP_SealUpdate() and EVP_SealFinal() have exactly the same
properties as the EVP_EncryptUpdate() and EVP_EncryptFi-
nal() routines, as documented on the EVP_EncryptInit(3)
EVP_SealInit() returns 0 on error or npubk if successful.
EVP_SealUpdate() and EVP_SealFinal() return 1 for success
and 0 for failure.
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.
openssl_evp(3), openssl_rand(3), EVP_EncryptInit(3),
2001-04-12 0.9.6g EVP_SealInit(3)
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