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Why does SSH 2.3 have problems interoperating with OpenSSH 2.1.1?

April 26, 2017interoperating OpenSSH problems SSH

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Why does SSH 2.3 have problems interoperating with OpenSSH 2.1.1?

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SSH 2.3 and earlier versions contain a flaw in their HMAC implementation. Their code was not supplying the full data block output from the digest, and instead always provided 128 bits. For longer digests, this caused SSH 2.3 to not interoperate with OpenSSH. OpenSSH 2.2.0 detects that SSH 2.3 has this flaw. Recent versions of SSH will have this bug fixed. Or you can add the following to SSH 2.3 sshd2_config.