1.\" $OpenBSD: EVP_PKEY_size.3,v 1.4 2024/12/06 12:51:13 schwarze Exp $ 2.\" full merge up to: OpenSSL eed9d03b Jan 8 11:04:15 2020 +0100 3.\" 4.\" This file is a derived work. 5.\" The changes are covered by the following Copyright and license: 6.\" 7.\" Copyright (c) 2022, 2023 Ingo Schwarze <schwarze@openbsd.org> 8.\" 9.\" Permission to use, copy, modify, and distribute this software for any 10.\" purpose with or without fee is hereby granted, provided that the above 11.\" copyright notice and this permission notice appear in all copies. 12.\" 13.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 14.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 15.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 16.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 17.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 18.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 19.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 20.\" 21.\" The original file was written by Richard Levitte <levitte@openssl.org>. 22.\" Copyright (c) 2020 The OpenSSL Project. All rights reserved. 23.\" 24.\" Redistribution and use in source and binary forms, with or without 25.\" modification, are permitted provided that the following conditions 26.\" are met: 27.\" 28.\" 1. Redistributions of source code must retain the above copyright 29.\" notice, this list of conditions and the following disclaimer. 30.\" 31.\" 2. Redistributions in binary form must reproduce the above copyright 32.\" notice, this list of conditions and the following disclaimer in 33.\" the documentation and/or other materials provided with the 34.\" distribution. 35.\" 36.\" 3. All advertising materials mentioning features or use of this 37.\" software must display the following acknowledgment: 38.\" "This product includes software developed by the OpenSSL Project 39.\" for use in the OpenSSL Toolkit. (http://www.openssl.org/)" 40.\" 41.\" 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to 42.\" endorse or promote products derived from this software without 43.\" prior written permission. For written permission, please contact 44.\" openssl-core@openssl.org. 45.\" 46.\" 5. Products derived from this software may not be called "OpenSSL" 47.\" nor may "OpenSSL" appear in their names without prior written 48.\" permission of the OpenSSL Project. 49.\" 50.\" 6. Redistributions of any form whatsoever must retain the following 51.\" acknowledgment: 52.\" "This product includes software developed by the OpenSSL Project 53.\" for use in the OpenSSL Toolkit (http://www.openssl.org/)" 54.\" 55.\" THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY 56.\" EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 57.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 58.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR 59.\" ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 60.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 61.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 62.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 63.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, 64.\" STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 65.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED 66.\" OF THE POSSIBILITY OF SUCH DAMAGE. 67.\" 68.Dd $Mdocdate: December 6 2024 $ 69.Dt EVP_PKEY_SIZE 3 70.Os 71.Sh NAME 72.Nm EVP_PKEY_size , 73.Nm EVP_PKEY_bits , 74.Nm EVP_PKEY_security_bits 75.Nd EVP_PKEY information functions 76.Sh SYNOPSIS 77.In openssl/evp.h 78.Ft int 79.Fo EVP_PKEY_size 80.Fa "const EVP_PKEY *pkey" 81.Fc 82.Ft int 83.Fo EVP_PKEY_bits 84.Fa "const EVP_PKEY *pkey" 85.Fc 86.Ft int 87.Fo EVP_PKEY_security_bits 88.Fa "const EVP_PKEY *pkey" 89.Fc 90.Sh DESCRIPTION 91.Fn EVP_PKEY_size 92returns the maximum size in bytes needed for the output buffer 93for almost any operation that can be done with 94.Fa pkey . 95The primary use is with 96.Xr EVP_SignFinal 3 97and 98.Xr EVP_SealInit 3 . 99The returned size is also large enough for the output buffer of 100.Xr EVP_PKEY_sign 3 , 101.Xr EVP_PKEY_encrypt 3 , 102.Xr EVP_PKEY_decrypt 3 , 103and 104.Xr EVP_PKEY_derive 3 . 105.Pp 106Unless the documentation for the operation says otherwise, 107the size returned by 108.Fn EVP_PKEY_size 109is only an upper limit and the final content of the target 110buffer may be smaller. 111It is therefore crucial to take note of the size given back by the 112function that performs the operation. 113For example, 114.Xr EVP_PKEY_sign 3 115returns that length in the 116.Pf * Fa siglen 117argument. 118.Pp 119Using 120.Fn EVP_PKEY_size 121is discouraged with 122.Xr EVP_DigestSignFinal 3 . 123.Pp 124Most functions using an output buffer support passing 125.Dv NULL 126for the buffer and a pointer to an integer 127to get the exact size that this function call delivers 128in the context that it is called in. 129This allows those functions to be called twice, once to find out the 130exact buffer size, then allocate the buffer in between, and call that 131function again to actually output the data. 132For those functions, it isn't strictly necessary to call 133.Fn EVP_PKEY_size 134to find out the buffer size, but it may still be useful in cases 135where it's desirable to know the upper limit in advance. 136.Pp 137.Fn EVP_PKEY_size 138is supported for the following algorithms: 139.Bl -column ED25519 "EVP_MAX_BLOCK_LENGTH = 32" 140.It Ta same result as from: 141.It CMAC Ta Dv EVP_MAX_BLOCK_LENGTH No = 32 142.It DH Ta Xr DH_size 3 143.It DSA Ta Xr DSA_size 3 144.It EC Ta Xr ECDSA_size 3 145.It ED25519 Ta 64, but see below 146.It HMAC Ta Dv EVP_MAX_MD_SIZE No = 64 147.It RSA Ta Xr RSA_size 3 148.It X25519 Ta Dv X25519_KEYLEN No = 32 149.El 150.Pp 151For 152.Dv EVP_PKEY_ED25519 , 153the situation is special: while the key size is 154.Dv ED25519_KEYLEN No = 32 bytes , 155.Fn EVP_PKEY_size 156returns 64 because the signature is longer than the keys. 157.Pp 158.Fn EVP_PKEY_bits 159returns the cryptographic length of the cryptosystem to which the key in 160.Fa pkey 161belongs, in bits. 162The definition of cryptographic length is specific to the key cryptosystem. 163The following algorithms are supported: 164.Bl -column ED25519 "the public domain parameter p" DSA_bits(3) 165.It Ta cryptographic length = Ta same result as from: 166.It Ta significant bits in ... Ta 167.It DH Ta the public domain parameter Fa p Ta Xr DH_bits 3 168.It DSA Ta the public domain parameter Fa p Ta Xr DSA_bits 3 169.It EC Ta the order of the group Ta Xr EC_GROUP_order_bits 3 170.It ED25519 Ta 253 Ta \(em 171.It RSA Ta the public modulus Ta Xr RSA_bits 3 172.It X25519 Ta 253 Ta \(em 173.El 174.Pp 175.Fn EVP_PKEY_security_bits 176returns the security strength measured in bits of the given 177.Fa pkey 178as defined in NIST SP800-57. 179The following algorithms are supported: 180.Bl -column ED25519 DSA_security_bits(3) 181.It Ta same result as from: 182.It DH Ta Xr DH_security_bits 3 183.It DSA Ta Xr DSA_security_bits 3 184.It EC Ta Xr EC_GROUP_order_bits 3 divided by 2 185.It ED25519 Ta 128 186.It RSA Ta Xr RSA_security_bits 3 187.It X25519 Ta 128 188.El 189.Pp 190For EC keys, if the result is greater than 80, it is rounded down 191to 256, 192, 128, 112, or 80. 192.Sh RETURN VALUES 193.Fn EVP_PKEY_size 194and 195.Fn EVP_PKEY_bits 196return a positive number or 0 if this size isn't available. 197.Pp 198.Fn EVP_PKEY_security_bits 199returns a number in the range from 0 to 256 inclusive 200or \-2 if this function is unsupported for the algorithm used by 201.Fa pkey . 202It returns 0 if 203.Fa pkey 204is 205.Dv NULL . 206.Sh SEE ALSO 207.Xr EVP_PKEY_decrypt 3 , 208.Xr EVP_PKEY_derive 3 , 209.Xr EVP_PKEY_encrypt 3 , 210.Xr EVP_PKEY_new 3 , 211.Xr EVP_PKEY_sign 3 , 212.Xr EVP_SealInit 3 , 213.Xr EVP_SignFinal 3 214.Sh HISTORY 215.Fn EVP_PKEY_size 216first appeared in SSLeay 0.6.0 and 217.Fn EVP_PKEY_bits 218in SSLeay 0.9.0. 219Both functions have been available since 220.Ox 2.4 . 221.Pp 222.Fn EVP_PKEY_security_bits 223first appeared in OpenSSL 1.1.0 and has been available since 224.Ox 7.2 . 225