Manual Reference Pages - EVP_SEALUPDATE (3)
EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption
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,
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 ciphers IV, as determined by (for
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
EVP_SealInit() returns 0 on error or npubk if successful.
EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for
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.
EVP_SealFinal() did not return a value before OpenSSL 0.9.7.
|1.0.1s ||EVP_SEALINIT (3) ||2016-03-01 |
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