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Diffstat (limited to 'doc/man3/EVP_PKEY_size.pod')
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diff --git a/doc/man3/EVP_PKEY_size.pod b/doc/man3/EVP_PKEY_size.pod new file mode 100644 index 000000000000..786c5039142c --- /dev/null +++ b/doc/man3/EVP_PKEY_size.pod @@ -0,0 +1,80 @@ +=pod + +=head1 NAME + +EVP_PKEY_size, EVP_PKEY_bits, EVP_PKEY_security_bits +- EVP_PKEY information functions + +=head1 SYNOPSIS + + #include <openssl/evp.h> + + int EVP_PKEY_size(const EVP_PKEY *pkey); + int EVP_PKEY_bits(const EVP_PKEY *pkey); + int EVP_PKEY_security_bits(const EVP_PKEY *pkey); + +=head1 DESCRIPTION + +EVP_PKEY_size() returns the maximum suitable size for the output +buffers for almost all operations that can be done with I<pkey>. +The primary documented use is with L<EVP_SignFinal(3)> and +L<EVP_SealInit(3)>, but it isn't limited there. The returned size is +also large enough for the output buffer of L<EVP_PKEY_sign(3)>, +L<EVP_PKEY_encrypt(3)>, L<EVP_PKEY_decrypt(3)>, L<EVP_PKEY_derive(3)>. + +It must be stressed that, unless the documentation for the operation +that's being performed says otherwise, the size returned by +EVP_PKEY_size() is only preliminary and not exact, so the final +contents of the target buffer may be smaller. It is therefore crucial +to take note of the size given back by the function that performs the +operation, such as L<EVP_PKEY_sign(3)> (the I<siglen> argument will +receive that length), to avoid bugs. + +EVP_PKEY_bits() returns the cryptographic length of the cryptosystem +to which the key in I<pkey> belongs, in bits. Note that the definition +of cryptographic length is specific to the key cryptosystem. + +EVP_PKEY_security_bits() returns the number of security bits of the given +I<pkey>, bits of security is defined in NIST SP800-57. + +=head1 RETURN VALUES + +EVP_PKEY_size(), EVP_PKEY_bits() and EVP_PKEY_security_bits() return a +positive number, or 0 if this size isn't available. + +=head1 NOTES + +Most functions that have an output buffer and are mentioned with +EVP_PKEY_size() have a functionality where you can pass NULL for the +buffer and still pass a pointer to an integer and get the exact size +that this function call delivers in the context that it's called in. +This allows those functions to be called twice, once to find out the +exact buffer size, then allocate the buffer in between, and call that +function again actually output the data. For those functions, it +isn't strictly necessary to call EVP_PKEY_size() to find out the +buffer size, but may be useful in cases where it's desirable to know +the upper limit in advance. + +It should also be especially noted that EVP_PKEY_size() shouldn't be +used to get the output size for EVP_DigestSignFinal(), according to +L<EVP_DigestSignFinal(3)/NOTES>. + +=head1 SEE ALSO + +L<EVP_SignFinal(3)>, +L<EVP_SealInit(3)>, +L<EVP_PKEY_sign(3)>, +L<EVP_PKEY_encrypt(3)>, +L<EVP_PKEY_decrypt(3)>, +L<EVP_PKEY_derive(3)> + +=head1 COPYRIGHT + +Copyright 2020 The OpenSSL Project Authors. All Rights Reserved. + +Licensed under the Apache License 2.0 (the "License"). You may not use +this file except in compliance with the License. You can obtain a copy +in the file LICENSE in the source distribution or at +L<https://www.openssl.org/source/license.html>. + +=cut |