Stunnel 5.48

Stunnel screenshotThe Stunnel software is developed to work like an SSL encryption wrapper among remote client and local or remote server. It can be used to add SSL a range of capabilities to mainly used internet services daemons like POP2, POP3, and IMAP servers without modifying the code of the program. Stunnel utilizes the OpenSSL library for cryptography, so it supports any cryptographic algorithms are assembled into the library.

Portability (Threading Models):

- PTHREAD (Posix)
- FORK (traditional Unix)
- UCONTEXT (userlevel)
- WIN32

Performance and scalability:

- Load sharing between multiple backend servers
- External session cache (for clusters)
- Compression (for narrow bandwidth)

Support for OpenSSL Security features:

- Access control with TLS-PSK and certificates
- CRL and OCSP certificate annulment
- SNI (Server Name Indication) support for name based virtual servers
- PFS (Perfect Forward Secrecy) with DH or ECDH key accord
- FIPS mode
- OpenSSL engines, including CAPI (Microsoft CryptoAPI)

Other Cross-platform features:

- Remote (socket) and local (inetd-style) method
- Load balancing remote targets with round-robin and priority strategies
- Redirection of SSL client connections on authentication failing
- IPv6 support
- TLS protocol negotiation for:
- cifs
- connect
- imap
- nntp
- pgsql
- pop3
- proxy
- smtp
- socks4, socks4a, socks5
- Delayed resolver (for dial-up connections or dynamic remote IP)
- Configuration file reloading
- Log file reopening
- UTF-8 configuration and log files
- Ident access control

Unix features:

- Unix socket support
- Socket activation with systemd feature
- Transparent proxy on preferred platforms
- Optional pseudo-terminal allocation for the local method
- Logging to syslog
- chroot (additional security)
- setuid and setgid (additional security)
- Libwrap (TCP Wrappers) access control
- EGD (Entropy Gathering Daemon) client

Windows features:

- GUI
- Saving cached peer certificate chains to files
- Windows service mode