Unable to connect to secure ftp server.

Question

When trying
ftp.Connect(hostName, port, SslMode.Explicit);
I am getting error: TlsException: Fatal error 'HandshakeFailure' has been reported by the remote connection end.

Here's the log
2020-04-09 16:13:23.858 INFO Ftp(1)[12] Response: 234 Proceed with negotiation.
2020-04-09 16:13:23.859 DEBUG Ftp(1)[12] Info: Upgrading control connection to TLS.
2020-04-09 16:13:23.923 DEBUG Ftp(1)[12] TLS: Using classic TLS core.
2020-04-09 16:13:23.944 DEBUG Ftp(1)[12] TLS: Enabled cipher suites: 0x000FFDF7FFE0E640.
2020-04-09 16:13:23.967 DEBUG Ftp(1)[12] TLS: Applicable cipher suites: 0x000FFDF7FFE0E640.
2020-04-09 16:13:23.975 DEBUG Ftp(1)[12] TLS: HandshakeMessage:ClientHello was sent.
2020-04-09 16:13:24.057 INFO Ftp(1)[12] TLS: Alert Alert:Alert was received.
2020-04-09 16:13:24.074 DEBUG Ftp(1)[12] TLS: Error while processing TLS packet: Rebex.Net.TlsException: Fatal error 'HandshakeFailure' has been reported by the remote connection end.
at pvhj.rhew(Byte[] fgw, Int32 fgx, Int32 fgy)
at pvhg.cskb(Byte[] bdi, Int32 bdj, Int32 bdk)
at pvhg.cskf()
2020-04-09 16:13:24.077 DEBUG Ftp(1)[12] TLS: Closing TLS socket.
2020-04-09 16:13:24.080 ERROR Ftp(1)[12] Info: Rebex.Net.TlsException: Fatal error 'HandshakeFailure' has been reported by the remote connection end. ---> Rebex.Net.TlsException: Fatal error 'HandshakeFailure' has been reported by the remote connection end. ---> Rebex.Net.TlsException: Fatal error 'HandshakeFailure' has been reported by the remote connection end.
at pvhj.rhew(Byte[] fgw, Int32 fgx, Int32 fgy)
at pvhg.cskb(Byte[] bdi, Int32 bdj, Int32 bdk)
at pvhg.cskf()
--- End of inner exception stack trace ---
at pvhg.cskf()
at pvhg.cskm()
at pvhd.qhtq()
at Rebex.Net.TlsSocket.tfpw()
at Rebex.Net.TlsSocket.Negotiate()
at gjon.gjmn(TlsParameters acu)
at Rebex.Net.Ftp.jhav(TlsParameters fj, FtpSecureUpgradeType fk)
at Rebex.Net.Ftp.jham(String fa, Int32 fb, TlsParameters fc, SslMode fd, FtpSecureUpgradeType fe)
--- End of inner exception stack trace ---
at Rebex.Net.Ftp.jham(String fa, Int32 fb, TlsParameters fc, SslMode fd, FtpSecureUpgradeType fe)

Answer 1

The server closed the connection just after receiving the ClientHello. This typically means that the client and server have no common TLS cipher suites, TLS versions, or similar.

I can suggest you for now to enable all TLS cipher suites and all TLS versions. It can be done like this:

ftp.Settings.SslAllowedSuites = TlsCipherSuite.All;
ftp.Settings.SslAllowedVersions = TlsVersion.Any;

Alternatively try also:

ftp.Settings.SslAllowedVersions = TlsVersion.TLS13;

Does server log contains some information about connection closure?

Are you able to connect to the server using any third-party application?

Comments

Eventually, I was able to get the info from the Server administrator.
Once Tls level and ciphers were coordinated, everything went well.

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Thank you for the info.