DataFlex

SFTP Set Allowed SSH Algorithms

Demonstrates the Chilkat SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH algorithms permitted for the connection. A JsonObject supplies comma-separated allow-lists for the kex, hostKey, cipher, and mac categories. It must be called before Connect.

Important: You typically should not set allowed algorithms explicitly. By default Chilkat orders algorithms according to best practices and accounts for known vulnerabilities.

Background: SSH negotiates a mutually supported algorithm from each category at connection time, and pinning that choice makes an application brittle: if a server later drops a weak algorithm or you point the code at a different server, the two sides may fail to agree and the connection breaks. The legitimate reasons to override are a security policy mandating specific algorithms, or a compatibility problem with an old server. Otherwise the safer default is to let the library's ordering evolve as guidance changes.

Chilkat DataFlex Downloads

Download Chilkat for DataFlex

DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoSftp
    Variant vJson
    Handle hoJson
    String sAllowed_kex
    String sAllowed_hostKey
    String sAllowed_cipher
    String sAllowed_mac
    Integer iPort
    String sTemp1

    Move False To iSuccess

    //  Demonstrates the SFtp.SetAllowedAlgorithms method, which configures the exact set of SSH
    //  algorithms permitted for the connection.  The only argument is a JsonObject.  It must be
    //  called before Connect.
    //  
    //  -------------------------------------------------------------------------------------------
    //  Note: You typically should NOT explicitly set allowed algorithms.
    //  By default, Chilkat orders algorithms according to best practices and accounts for known
    //  vulnerabilities such as the "Terrapin Attack".  Hard-coding algorithms can make an
    //  application brittle over time: if a server later changes its allowed algorithms, or if you
    //  connect to a different server, the client and server may fail to agree on a mutually
    //  supported set.
    //  -------------------------------------------------------------------------------------------

    Get Create (RefClass(cComChilkatSFtp)) To hoSftp
    If (Not(IsComObjectCreated(hoSftp))) Begin
        Send CreateComObject of hoSftp
    End

    Get Create (RefClass(cComChilkatJsonObject)) To hoJson
    If (Not(IsComObjectCreated(hoJson))) Begin
        Send CreateComObject of hoJson
    End

    //  The algorithms supported by Chilkat, by category:
    //  
    //  Key-exchange:
    //    curve25519-sha256
    //    curve25519-sha256@libssh.org
    //    ecdh-sha2-nistp256
    //    ecdh-sha2-nistp384
    //    ecdh-sha2-nistp521
    //    diffie-hellman-group14-sha256
    //    diffie-hellman-group16-sha512
    //    diffie-hellman-group18-sha512
    //    diffie-hellman-group-exchange-sha256
    //    diffie-hellman-group1-sha1
    //    diffie-hellman-group14-sha1
    //    diffie-hellman-group-exchange-sha1
    //  
    //  Host key:
    //    ssh-ed25519
    //    ecdsa-sha2-nistp256
    //    ecdsa-sha2-nistp384
    //    ecdsa-sha2-nistp521
    //    rsa-sha2-256
    //    rsa-sha2-512
    //    ssh-rsa
    //    ssh-dss
    //  
    //  Cipher (encryption):
    //    chacha20-poly1305@openssh.com
    //    aes128-ctr
    //    aes256-ctr
    //    aes192-ctr
    //    aes128-cbc
    //    aes256-cbc
    //    aes192-cbc
    //    aes128-gcm@openssh.com
    //    aes256-gcm@openssh.com
    //    twofish256-cbc
    //    twofish128-cbc
    //    blowfish-cbc
    //  
    //  MAC (hash):
    //    hmac-sha2-256
    //    hmac-sha2-512
    //    hmac-sha2-256-etm@openssh.com
    //    hmac-sha2-512-etm@openssh.com
    //    hmac-sha1-etm@openssh.com
    //    hmac-sha1
    //    hmac-ripemd160
    //    hmac-sha1-96
    //    hmac-md5

    //  List the allowed key-exchange, host-key, cipher (encryption), and mac (hash) algorithms, in
    //  order of preference.
    Move "curve25519-sha256@libssh.org,ecdh-sha2-nistp256" To sAllowed_kex
    Move "ssh-ed25519,ecdsa-sha2-nistp256" To sAllowed_hostKey
    Move "chacha20-poly1305@openssh.com,aes256-ctr" To sAllowed_cipher
    Move "hmac-sha2-256,hmac-sha2-512" To sAllowed_mac

    Get ComUpdateString Of hoJson "kex" sAllowed_kex To iSuccess
    Get ComUpdateString Of hoJson "hostKey" sAllowed_hostKey To iSuccess
    Get ComUpdateString Of hoJson "cipher" sAllowed_cipher To iSuccess
    Get ComUpdateString Of hoJson "mac" sAllowed_mac To iSuccess

    //  Apply the allow-list before connecting.
    Get pvComObject of hoJson to vJson
    Get ComSetAllowedAlgorithms Of hoSftp vJson To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Move 22 To iPort
    Get ComConnect Of hoSftp "sftp.example.com" iPort To iSuccess
    If (iSuccess = False) Begin
        Get ComLastErrorText Of hoSftp To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    Showln "Connected."

    Send ComDisconnect To hoSftp


End_Procedure