On 01/11/2019 11:59, pablo platt wrote: > Thank you for the explanation. > > The use case is a WebRTC server (SFU) that encrypts and authenticate > SRTP packets. > Encryption is a major part of CPU load on SFU servers. Reducing it by > 50% will have a large impact. > > Is it planned to add aes-128-hmac-sha1 encrypt-then-mac? There are no current plans. You might investigate the impact of using AEAD ciphers instead. Matt > > On Fri, Nov 1, 2019 at 1:32 PM Matt Caswell <matt@xxxxxxxxxxx > <mailto:matt@xxxxxxxxxxx>> wrote: > > > > On 01/11/2019 07:56, pablo platt wrote: > > Hi, > > > > Stitching aes-cbc with sha1 can result with x2 performance [1]. > > Is there support for stitched aes-128-hmac-sha1 encrypt-then-mac? This > > issue [2] says that only mac-then-encrypt is supported in OpenSSL. > > The issue is correct. Only mac-then-encrypt is supported. Furthermore > these stitched ciphers are specifically targeted at use by libssl and > are designed for use in SSL/TLS only. They are not general purpose > ciphers and should not be used directly unless you *really* know what > you are doing. > > Note that more modern TLS ciphersuites use AEAD modes such as GCM or CCM > so that mac-then-encrypt vs encrypt-then-mac and "stitched" ciphers are > irrelevant anyway. > > > > > Does this implement mac-then-encrypt and relevant [3]? > > [3] is the aesni assembler implementation used behind the > EVP_aes_128_cbc_hmac_sha1() and EVP_aes_256_cbc_hmac_sha1() ciphers, > i.e. all the same comments I made above apply here. It's > mac-then-encrypt, and specifically targeted for use in SSL/TLS by > libssl. It's not intended for general purpose use. > > The documentation says this about these ciphers: > > "EVP_aes_128_cbc_hmac_sha1(), > EVP_aes_256_cbc_hmac_sha1() > > Authenticated encryption with AES in CBC mode using SHA-1 as HMAC, with > keys of 128 and 256 bits length respectively. The authentication tag is > 160 bits long. > > WARNING: this is not intended for usage outside of TLS and requires > calling of some undocumented ctrl functions. These ciphers do not > conform to the EVP AEAD interface." > > https://www.openssl.org/docs/man1.1.1/man3/EVP_aes_128_cbc_hmac_sha1.html > > > > > Is it possible to use the same code with just changing the order to > > achieve encrypt-then-mac? > > No. > > > How can I compile the Perl file to be used from a C program? > > This is an internal file not intended for use outside of OpenSSL and not > intended to be compiled separately. You might be able to extract it - > but if so, you're on your own. > > > Matt >
