| S/MIME | Secure/Multipurpose Internet Mail Extensions |
| S2ML | Security Services Markup Language |
| SASL | Simple Authentication and Security Layer |
| SDK | Software Development Kit |
| SHA-1 | Secure Hash Algorithm V1 |
| SHA1withDSA | SHA-1 with Digital Signature Algorithm |
| SMTP | Simple Mail Transfer Protocol |
| SNA | Systems Network Architecture |
| SOAP | Simple Object Access Protocol |
| SOCKS | SOCKet Secure |
| SPI | service provider interface |
| SQLJ | Structured Query Language for Java |
| SSL | Secure Sockets Layer |
| SSO | single sign-on |