The behavior of NSS for renegotiation can be changed through API function calls, or with the following environment variables:

• NSS_SSL_ENABLE_RENEGOTIATION
  • values:
    • [0|n|N]: SSL_RENEGOTIATE_NEVER
      • Never allow renegotiation - That was the default for 3.12.5 release.
    • [1|u|U]: SSL_RENEGOTIATE_UNRESTRICTED
      • Server and client are allowed to renegotiate without any restrictions. This setting was the default prior 3.12.5 and makes products vulnerable.
    • [2|r|R]: SSL_RENEGOTIATE_REQUIRES_XTN (default)
      • Only allows renegotiation if the peer's hello bears the TLS renegotiation_info extension. This is the safe renegotiation.
    • [3|t|T]: SSL_RENEGOTIATE_TRANSITIONAL
      • Disallows unsafe renegotiation in server sockets only, but allows clients to continue to renegotiate with vulnerable servers. This value should only be used during the transition period when few servers have been upgraded.
• NSS_SSL_REQUIRE_SAFE_NEGOTIATION
  • values:
    • 1: requireSafeNegotiation = TRUE
    • unset: requireSafeNegotiation = FALSE
    Controls whether safe renegotiation indication is required for initial handshake. If TRUE, a connection will be dropped at initial handshake if the peer server or client does not support safe renegotiation. The default setting for this option is FALSE.

These options can also be set with the following SSL options:

• sslOptions.enableRenegotiation
• sslOptions.requireSafeNegotiation
• New pseudo cipher suite value: TLS_EMPTY_RENEGOTIATION_INFO_SCSV (cannot be negotiated)

Note: The TLS Server Name Indication for clients is already fully implemented in NSS.

• New functions for SNI (see ssl.h for more information):
  • SSLSNISocketConfig
    • Return values:
      • SSL_SNI_CURRENT_CONFIG_IS_USED: libSSL must use the default cert and key.
      • SSL_SNI_SEND_ALERT: libSSL must send the "unrecognized_name" alert.
  • SSL_SNISocketConfigHook
  • SSL_ReconfigFD
  • SSL_ConfigServerSessionIDCacheWithOpt
  • SSL_SetTrustAnchors
  • SSL_GetNegotiatedHostInfo
• New enum for SNI:
  • SSLSniNameType (see sslt.h)

• CERTDistNames: Duplicate distinguished name array.
• CERT_DistNamesFromCertList: Generate an array of Distinguished names from a list of certs.

• CERT_CacheOCSPResponseFromSideChannel:
  • This function is intended for use when OCSP responses are provided via a side-channel, i.e. TLS OCSP stapling (a.k.a. the status_request extension).

• SSL_GetImplementedCiphers
• SSL_GetNumImplementedCiphers
• SSL_HandshakeNegotiatedExtension

• SSL_ERROR_UNSAFE_NEGOTIATION
• SSL_ERROR_RX_UNEXPECTED_UNCOMPRESSED_RECORD

• SSLExtensionType

• 1 means force always use proxy, 0 means never use proxy, NULL means use proxy for non-local files only.

• Key log file. If set, NSS logs RSA pre-master secrets to this file. This allows packet sniffers to decrypt TLS connections.
  See documentation.
  Note: The code must be built with TRACE defined to use this functionality.