1=pod 2 3=head1 NAME 4 5EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption 6 7=head1 SYNOPSIS 8 9 #include <openssl/evp.h> 10 11 int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, 12 unsigned char **ek, int *ekl, unsigned char *iv, 13 EVP_PKEY **pubk, int npubk); 14 int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, 15 int *outl, unsigned char *in, int inl); 16 int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out, 17 int *outl); 18 19=head1 DESCRIPTION 20 21The EVP envelope routines are a high level interface to envelope 22encryption. They generate a random key and IV (if required) then 23"envelope" it by using public key encryption. Data can then be 24encrypted using this key. 25 26EVP_SealInit() initializes a cipher context B<ctx> for encryption 27with cipher B<type> using a random secret key and IV. B<type> is normally 28supplied by a function such as EVP_aes_256_cbc(). The secret key is encrypted 29using one or more public keys, this allows the same encrypted data to be 30decrypted using any of the corresponding private keys. B<ek> is an array of 31buffers where the public key encrypted secret key will be written, each buffer 32must contain enough room for the corresponding encrypted key: that is 33B<ek[i]> must have room for B<EVP_PKEY_size(pubk[i])> bytes. The actual 34size of each encrypted secret key is written to the array B<ekl>. B<pubk> is 35an array of B<npubk> public keys. 36 37The B<iv> parameter is a buffer where the generated IV is written to. It must 38contain enough room for the corresponding cipher's IV, as determined by (for 39example) EVP_CIPHER_iv_length(type). 40 41If the cipher does not require an IV then the B<iv> parameter is ignored 42and can be B<NULL>. 43 44EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties 45as the EVP_EncryptUpdate() and EVP_EncryptFinal() routines, as 46documented on the L<EVP_EncryptInit(3)|EVP_EncryptInit(3)> manual 47page. 48 49=head1 RETURN VALUES 50 51EVP_SealInit() returns 0 on error or B<npubk> if successful. 52 53EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for 54failure. 55 56=head1 NOTES 57 58Because a random secret key is generated the random number generator 59must be seeded before calling EVP_SealInit(). 60 61The public key must be RSA because it is the only OpenSSL public key 62algorithm that supports key transport. 63 64Envelope encryption is the usual method of using public key encryption 65on large amounts of data, this is because public key encryption is slow 66but symmetric encryption is fast. So symmetric encryption is used for 67bulk encryption and the small random symmetric key used is transferred 68using public key encryption. 69 70It is possible to call EVP_SealInit() twice in the same way as 71EVP_EncryptInit(). The first call should have B<npubk> set to 0 72and (after setting any cipher parameters) it should be called again 73with B<type> set to NULL. 74 75=head1 SEE ALSO 76 77L<evp(3)|evp(3)>, L<rand(3)|rand(3)>, 78L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>, 79L<EVP_OpenInit(3)|EVP_OpenInit(3)> 80 81=head1 HISTORY 82 83EVP_SealFinal() did not return a value before OpenSSL 0.9.7. 84 85=cut 86