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81 lines
2.9 KiB
Plaintext
81 lines
2.9 KiB
Plaintext
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=pod
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=head1 NAME
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EVP_PKEY_size, EVP_PKEY_bits, EVP_PKEY_security_bits
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- EVP_PKEY information functions
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=head1 SYNOPSIS
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#include <openssl/evp.h>
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int EVP_PKEY_size(const EVP_PKEY *pkey);
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int EVP_PKEY_bits(const EVP_PKEY *pkey);
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int EVP_PKEY_security_bits(const EVP_PKEY *pkey);
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=head1 DESCRIPTION
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EVP_PKEY_size() returns the maximum suitable size for the output
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buffers for almost all operations that can be done with I<pkey>.
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The primary documented use is with L<EVP_SignFinal(3)> and
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L<EVP_SealInit(3)>, but it isn't limited there. The returned size is
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also large enough for the output buffer of L<EVP_PKEY_sign(3)>,
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L<EVP_PKEY_encrypt(3)>, L<EVP_PKEY_decrypt(3)>, L<EVP_PKEY_derive(3)>.
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It must be stressed that, unless the documentation for the operation
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that's being performed says otherwise, the size returned by
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EVP_PKEY_size() is only preliminary and not exact, so the final
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contents of the target buffer may be smaller. It is therefore crucial
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to take note of the size given back by the function that performs the
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operation, such as L<EVP_PKEY_sign(3)> (the I<siglen> argument will
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receive that length), to avoid bugs.
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EVP_PKEY_bits() returns the cryptographic length of the cryptosystem
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to which the key in I<pkey> belongs, in bits. Note that the definition
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of cryptographic length is specific to the key cryptosystem.
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EVP_PKEY_security_bits() returns the number of security bits of the given
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I<pkey>, bits of security is defined in NIST SP800-57.
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=head1 RETURN VALUES
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EVP_PKEY_size(), EVP_PKEY_bits() and EVP_PKEY_security_bits() return a
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positive number, or 0 if this size isn't available.
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=head1 NOTES
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Most functions that have an output buffer and are mentioned with
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EVP_PKEY_size() have a functionality where you can pass NULL for the
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buffer and still pass a pointer to an integer and get the exact size
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that this function call delivers in the context that it's called in.
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This allows those functions to be called twice, once to find out the
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exact buffer size, then allocate the buffer in between, and call that
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function again actually output the data. For those functions, it
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isn't strictly necessary to call EVP_PKEY_size() to find out the
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buffer size, but may be useful in cases where it's desirable to know
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the upper limit in advance.
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It should also be especially noted that EVP_PKEY_size() shouldn't be
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used to get the output size for EVP_DigestSignFinal(), according to
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L<EVP_DigestSignFinal(3)/NOTES>.
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=head1 SEE ALSO
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L<EVP_SignFinal(3)>,
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L<EVP_SealInit(3)>,
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L<EVP_PKEY_sign(3)>,
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L<EVP_PKEY_encrypt(3)>,
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L<EVP_PKEY_decrypt(3)>,
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L<EVP_PKEY_derive(3)>
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=head1 COPYRIGHT
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Copyright 2020 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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