Oh, yep, they updated to OpenSSL-1 in 5.1.0.
I'll probably do a proper KT OpenSSH (where sftp-server comes from) build at some point, so, err, unless you want to do it yourself, you'll have to wait, because the older Kindles relies on a binary built against OpenSSL-0.9.8 (and I guess that's where the binary came from, the K2/K3 usbnet hack).
(The very, very ugly hack of symlinking openssl 1 to openssl 0.9.8 might work, but it might also make sftp-server explode in a fiery abi mismatch ^^).
But that's good to know, it means that yet another thing will be 5.1.0 only

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