FlashFXP FTPES Client Certificate handshake failure

msg7086 · 12-20-2017, 03:23 PM

Yes, I know this post may be useless considering what has happened. But I still want to share this with you and, if possible, get some ideas from you.

I'm trying to set up FTP server with client certificate authentication. I'm using ProFTPd 1.3.5b.

On the server my configuration reads:

Code:

TLSEngine                               on
TLSProtocol                             SSLv23 TLSv1 TLSv1.2
TLSECCertificateFile                    /etc/ssl/ssl.crt
TLSECCertificateKeyFile                 /etc/ssl/ssl.key
TLSRequired                             ctrl
TLSCACertificateFile                    /etc/ssl/ca.crt
TLSVerifyClient                         on
TLSOptions                              AllowDotLogin

Where ca.crt is a self-signed ECDSA-SHA256 CA with a EC-384 key.

Client keys are generated and signed by the CA.

When connecting to the FTPES server from FlashFXP 5.4, it is unable to complete ssl handshake.

Code:

[15:12:35] [R] Connected to test ftp
[15:12:35] [R] 220 ProFTPD 1.3.5b Server (Debian) [::ffff:172.16.0.102]
[15:12:35] [R] AUTH TLS
[15:12:35] [R] 234 AUTH TLS successful
[15:12:35] [R] SSL error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake failure
[15:12:36] [R] Failed TLSv1 negotiation, disconnected
[15:12:36] [R] Connection failed (Connection closed by server)
[15:12:36] [R] Delaying for 10 seconds before reconnect attempt #1

Having tried explicitly specifying SSLv3 or TLSv1 or TLSv1.2 and none of the three works.

However a manual test using openssl CLI shows that the server is working fine.

Code:

D:\>openssl s_client -connect <<removed>> -starttls ftp -cert <<removed>>-ftp.crt -key <<removed>>-ftp.key
CONNECTED(00000158)
depth=0 CN = <<removed>>.com
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 CN = <<removed>>.com
verify error:num=21:unable to verify the first certificate
verify return:1
---
Certificate chain
 0 s:/CN=<<removed>>.com
   i:/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
---
Server certificate
-----BEGIN CERTIFICATE-----
MIIENjCCAx6gAwIBAgISBLTsG9cQFS5GIqfAG2EVLjbTMA0GCSqGSIb3DQEBCwUA
<<removed>>
VxhOxUBUHrvNvG1a/102TDGQu+LGDyBUe40=
-----END CERTIFICATE-----
subject=/CN=<<removed>>.com
issuer=/C=US/O=Let's Encrypt/CN=Let's Encrypt Authority X3
---
Acceptable client certificate CA names
/CN=<<removed>>CA
Client Certificate Types: RSA sign, DSA sign, ECDSA sign
Requested Signature Algorithms: RSA+SHA512:DSA+SHA512:ECDSA+SHA512:RSA+SHA384:DSA+SHA384:ECDSA+SHA384:RSA+SHA256:DSA+SHA256:ECDSA+SHA256:RSA+SHA224:DSA+SHA224:ECDSA+SHA224:RSA+SHA1:DSA+SHA1:ECDSA+SHA1
Shared Requested Signature Algorithms: RSA+SHA512:DSA+SHA512:ECDSA+SHA512:RSA+SHA384:DSA+SHA384:ECDSA+SHA384:RSA+SHA256:DSA+SHA256:ECDSA+SHA256:RSA+SHA224:DSA+SHA224:ECDSA+SHA224:RSA+SHA1:DSA+SHA1:ECDSA+SHA1
Peer signing digest: SHA512
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 1556 bytes and written 1379 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-ECDSA-AES256-GCM-SHA384
Server public key is 256 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-ECDSA-AES256-GCM-SHA384
    Session-ID: <<removed>>
    Session-ID-ctx:
    Master-Key: <<removed>>
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    Start Time: 1513797526
    Timeout   : 300 (sec)
    Verify return code: 21 (unable to verify the first certificate)
---
220 ProFTPD 1.3.5b Server (Debian) [::ffff:172.16.0.102]
user root
232 User root logged in
stat -al
211-Status of .:
211-<<removed>>
211 End of status
quit
221 Goodbye.
closed

Both RSA-2048 and EC-384 key pairs were tried, and results were the same.