85 lines
3 KiB
Text
85 lines
3 KiB
Text
=pod
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=head1 NAME
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EVP_SealInit, EVP_SealUpdate, EVP_SealFinal - EVP envelope encryption
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_SealInit(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type,
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unsigned char **ek, int *ekl, unsigned char *iv,
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EVP_PKEY **pubk, int npubk);
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int EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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int EVP_SealFinal(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl);
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=head1 DESCRIPTION
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The EVP envelope routines are a high level interface to envelope
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encryption. They generate a random key and IV (if required) then
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"envelope" it by using public key encryption. Data can then be
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encrypted using this key.
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EVP_SealInit() initializes a cipher context B<ctx> for encryption
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with cipher B<type> using a random secret key and IV. B<type> is normally
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supplied by a function such as EVP_des_cbc(). The secret key is encrypted
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using one or more public keys, this allows the same encrypted data to be
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decrypted using any of the corresponding private keys. B<ek> is an array of
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buffers where the public key encrypted secret key will be written, each buffer
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must contain enough room for the corresponding encrypted key: that is
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B<ek[i]> must have room for B<EVP_PKEY_size(pubk[i])> bytes. The actual
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size of each encrypted secret key is written to the array B<ekl>. B<pubk> is
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an array of B<npubk> public keys.
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The B<iv> parameter is a buffer where the generated IV is written to. It must
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contain enough room for the corresponding cipher's IV, as determined by (for
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example) EVP_CIPHER_iv_length(type).
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If the cipher does not require an IV then the B<iv> parameter is ignored
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and can be B<NULL>.
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EVP_SealUpdate() and EVP_SealFinal() have exactly the same properties
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as the EVP_EncryptUpdate() and EVP_EncryptFinal() routines, as
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documented on the L<EVP_EncryptInit(3)|EVP_EncryptInit(3)> manual
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page.
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=head1 RETURN VALUES
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EVP_SealInit() returns 0 on error or B<npubk> if successful.
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EVP_SealUpdate() and EVP_SealFinal() return 1 for success and 0 for
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failure.
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=head1 NOTES
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Because a random secret key is generated the random number generator
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must be seeded before calling EVP_SealInit().
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The public key must be RSA because it is the only OpenSSL public key
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algorithm that supports key transport.
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Envelope encryption is the usual method of using public key encryption
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on large amounts of data, this is because public key encryption is slow
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but symmetric encryption is fast. So symmetric encryption is used for
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bulk encryption and the small random symmetric key used is transferred
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using public key encryption.
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It is possible to call EVP_SealInit() twice in the same way as
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EVP_EncryptInit(). The first call should have B<npubk> set to 0
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and (after setting any cipher parameters) it should be called again
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with B<type> set to NULL.
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=head1 SEE ALSO
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L<evp(3)|evp(3)>, L<rand(3)|rand(3)>,
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L<EVP_EncryptInit(3)|EVP_EncryptInit(3)>,
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L<EVP_OpenInit(3)|EVP_OpenInit(3)>
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=head1 HISTORY
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EVP_SealFinal() did not return a value before OpenSSL 0.9.7.
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=cut
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