EVP_SealInit, EVP_SealUpdate, EVP_SealFinal — EVP envelope encryption
EVP_SealInit(EVP_CIPHER_CTX *ctx, EVP_CIPHER *type, unsigned char
**ek, int *ekl, unsigned char *iv,EVP_PKEY **pubk, int npubk);
EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
unsigned char *in, int inl);
*ctx, unsigned char *out, int *outl);
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
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.
EVP_SealInit() returns 0 on error or npubk if
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.
evp(3), rand(3), EVP_EncryptInit(3), EVP_OpenInit(3)
EVP_SealFinal() did not return a value before OpenSSL 0.9.7.