ssh-dss
```

`--sftp=kex-algos=...` specifies the supported key-exchange algorithms in preference order.

Valid values: 

```
curve25519-sha256
******@****.***
ecdh-sha2-nistp256
ecdh-sha2-nistp384
ecdh-sha2-nistp521
diffie-hellman-group14-sha256
diffie-hellman-group16-sha512
diffie-hellman-group14-sha1
diffie-hellman-group1-sha1
```

// ciphers for backward compatibility. In particular, AES-CBC
// and non-ECDHE ciphers.
func TLSCiphersBackwardCompatible() []uint16 {
	return []uint16{
		tls.TLS_CHACHA20_POLY1305_SHA256, // TLS 1.3
		tls.TLS_AES_128_GCM_SHA256,
		tls.TLS_AES_256_GCM_SHA384,
		tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256, // TLS 1.2 ECDHE GCM / POLY1305
		tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256,