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The manual pages require for some API functions that the 'random number generator must be seeded' before calling the function. Initially, this was meant literally, i.e. the OpenSSL CSPRNG had to be seeded manually before calling these functions. Since version 1.1.1, the CSPRNG is seeded automatically on first use, so it's not the responsibility of the programmer anymore. Still, he needs to be aware that the seeding might fail. Reviewed-by: Paul Dale <paul.dale@oracle.com> Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org> (Merged from https://github.com/openssl/openssl/pull/9257)
93 lines
3.4 KiB
Plaintext
93 lines
3.4 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, 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, 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_aes_256_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)> 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 when EVP_SealInit() is called.
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If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
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external circumstances (see L<RAND(7)>), the operation will fail.
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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(7)>, L<RAND_bytes(3)>,
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L<EVP_EncryptInit(3)>,
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L<EVP_OpenInit(3)>,
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L<RAND(7)>
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=head1 COPYRIGHT
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Copyright 2000-2016 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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