When the key exchange produces less key material than is needed for the cipher or hmac
algorithms, there is an iterative procedure to produce more.
For example, a SHA-1 key exchange algorithm produces 20 bytes of key material.
A SHA-256 hmac uses a 32 byte key, so one iteration of the procedure produces another
20 bytes of key material for a total of 40 which is sufficient for the hmac key.
The library works correctly in such cases of one iteration, but the logic is wrong if
more than one iteration is needed. In #1660, the connection uses a SHA-1 kex algorithm
with a SHA-512 hmac (64 byte key), requiring 3 iterations of the extension procedure and
resulting in an error upon connection.
This change fixes the logic to use the output of the previous iteration per the spec.
closes#1660
This drops some of the algorithms long-considered legacy/insecure.
The idea is both to improve the theoretical security of the library by not offering
these algorithms, and to improve the practical security of the library by not having
hand-written, barely tested crypto code.
The overarching goal is for the library to have minimal exposure to crypto
implementation, relying firstly on the .NET base libraries, and secondly on
third-party providers, such as BouncyCastle.
This change covers deleting the cipher algorithms arcfour, blowfish, twofish, cast.
It covers deleting the MD5-based and truncated HMAC algorithms.
These were all disabled in OpenSSH server (sshd) in 2014[^1]:
> sshd(8): The default set of ciphers and MACs has been altered to
> remove unsafe algorithms. In particular, CBC ciphers and arcfour*
> are disabled by default.
>
> The full set of algorithms remains available if configured
> explicitly via the Ciphers and MACs sshd_config options.
and in the client in 2016[^2]:
> This release disables a number of legacy cryptographic algorithms
> by default in ssh:
>
> * Several ciphers blowfish-cbc, cast128-cbc, all arcfour variants
> and the rijndael-cbc aliases for AES.
>
> * MD5-based and truncated HMAC algorithms.
>
> These algorithms are already disabled by default in sshd.
This change also drops PKCS5Padding, which is a line-for-line copy of PKCS7Padding,
and StreamCipher, which is now unused (and useless anyway).
[^1]: https://www.openssh.com/txt/release-6.7
[^2]: https://www.openssh.com/txt/release-7.2
Co-authored-by: Wojciech Nagórski <wojtpl2@gmail.com>
* Support ETM (Encrypt-then-MAC) variants for HMAC
* Support ETM (Encrypt-then-MAC) variants for HMAC
* Remove `ETM` property from `HashInfo`
* Add support for HmacMd5Etm, HmacMd5_96_Etm, HmacSha1Etm and HmacSha1_96_Etm
Explicitly specify etm even if false
* Add Encrypt-then-MAC variants to README.md
* Add back empty span to prevent auto link
* Store ETM in `HashInfo`;
Change `HMAC Create[...]Hash()` to `HashAlgorithm Create[...]Hash(out bool isEncryptThenMAC)`
* Move test projects to test folder.
Move global.json to root of repo.
Update solution items in solution.
* Move test projects to test folder.
Move global.json to root of repo.
Update solution items in solution.
Update appveyor configuration/
* Attempt to have appveyor use the correct .NET SDK.
* Update .NET SDK to version 7.0.402.
* Move Data folder below Renci.SshNet.Tests.
* Make csinst less chatty.
* Move Data folder directly below test folder as it's used by multiple test projects.
* Remove CS1591 nowarn from concrete test projects as this is already defined in the Directory.Build.props that is in the test folder.
* Fix integration test after moving test projects
---------
Co-authored-by: drieseng <gert.driesen@telenet.be>
Rob Hague