Use System.Security.Cryptography in AesCipher

[Rob-Hague]

System.Security.Cryptography.Aes is supported on all target platforms (it wasn't in previous versions of the library). So we can use it rather than the hand-written code.

The change comes with modest performance gains (#865 (comment)) and from a maintenance perspective, makes it easier to achieve the design proposed in the linked comment in order to get much greater performance gains.

[WojciechNagorski]

I'm really impressed this is a great job!
Can you describe how this PRis related with #865 ?
Can you provide some Benchmark results?

[Rob-Hague]

I would expect this to become the implementation of SshNetCipherModeImpl in the proposal in #865 (comment), which would be used when using the constructor taking Renci.SshNet.Security.Ciphers.CipherMode. #865 would provide a much faster implementation when using a new constructor taking a System.Security.Cryptography.CipherMode value.

Reposting the benchmarks here (they are the same as in the linked comment)

Results on develop branch 826222f:

Method	Mean	Error	StdDev	Gen0	Allocated
Encrypt_CBC	320.4 μs	0.47 μs	0.36 μs	15.6250	32.41 KB
Decrypt_CBC	352.3 μs	2.37 μs	1.85 μs	15.6250	32.41 KB
Encrypt_CFB	335.6 μs	0.43 μs	0.34 μs	15.6250	32.45 KB
Decrypt_CFB	367.9 μs	4.23 μs	3.95 μs	15.6250	32.45 KB
Encrypt_CTR	310.4 μs	0.38 μs	0.31 μs	15.6250	32.45 KB
Decrypt_CTR	315.3 μs	3.96 μs	3.70 μs	15.6250	32.45 KB

Results on these changes:

Method	Mean	Error	StdDev	Gen0	Allocated
Encrypt_CBC	221.2 μs	2.01 μs	1.88 μs	15.8691	32.7 KB
Decrypt_CBC	220.0 μs	2.73 μs	2.56 μs	15.8691	32.71 KB
Encrypt_CFB	251.3 μs	0.33 μs	0.27 μs	15.6250	32.75 KB
Decrypt_CFB	255.3 μs	0.67 μs	0.60 μs	15.6250	32.75 KB
Encrypt_CTR	201.3 μs	0.41 μs	0.38 μs	15.8691	32.75 KB
Decrypt_CTR	209.3 μs	0.22 μs	0.19 μs	15.8691	32.75 KB

Results on #865zybexXL@a9f68fb:

Method	Mean	Error	StdDev	Gen0	Allocated
Encrypt_CBC	29.637 μs	0.1278 μs	0.1067 μs	16.1133	33.14 KB
Decrypt_CBC	6.579 μs	0.0160 μs	0.0142 μs	16.1285	33.14 KB
Encrypt_CFB	333.761 μs	0.1710 μs	0.1335 μs	15.6250	32.52 KB
Decrypt_CFB	333.899 μs	0.2090 μs	0.1955 μs	15.6250	32.52 KB
Encrypt_CTR	24.630 μs	0.0327 μs	0.0273 μs	78.1250	161.2 KB
Decrypt_CTR	24.544 μs	0.0817 μs	0.0683 μs	78.1250	161.2 KB

The allocations in CTR mode can easily be removed, and I would expect it to extend to CFB as well. So given how much faster it is, it will be worth having as an implementation. The proposal is to keep the implementations separate so that we keep using a Renci.SshNet.Security.Ciphers.CipherMode if it is provided.

[zybexXL]

@WojciechNagorski I've restructured #865 to incorporate suggestions from Rob-Hague in the above linked comment. This makes both PRs functionally similar, but #865 is much faster as this one only accelerates blockwise encryption/decryption, while 865 also accelerates one-shot buffer operations.

#865 already used acceleration (2 years ago) but the code was injected into the CipherMode classes instead of AesCipher.cs. I've now refactored and improved it.

[WojciechNagorski]

@Rob-Hague, @zybexXL Which of these two PRs should be checked first? #1235#865 They are related and I don't really know where to start.

[WojciechNagorski]

I like this kind of PR

[WojciechNagorski]

The 2023.0.1 version has been released to Nuget: https://www.nuget.org/packages/SSH.NET/2023.0.1