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77 lines
2.6 KiB
Plaintext
77 lines
2.6 KiB
Plaintext
=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, EVP_CIPHER *type, unsigned char **ek,
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int *ekl, unsigned char *iv,EVP_PKEY **pubk, int npubk);
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void EVP_SealUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out,
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int *outl, unsigned char *in, int inl);
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void 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 then "envelope" it by
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using public key encryption. Data can then be encrypted using this
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key.
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EVP_SealInit() initialises a cipher context B<ctx> for encryption
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with cipher B<type> using a random secret key and IV supplied in
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the B<iv> parameter. B<type> is normally supplied by a function such
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as EVP_des_cbc(). The secret key is encrypted using one or more public
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keys, this allows the same encrypted data to be decrypted using any
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of the corresponding private keys. B<ek> is an array of buffers where
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the public key encrypted secret key will be written, each buffer must
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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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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 -1 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 paramaters) 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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=cut
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