Pidgin-sipe failed to authenticate to server while connecting to Office 365

For the last few days, an increasing number of Pidgin-sipe users have been rejected while trying to connect to their Office 365 accounts.
According to the SIPE developers, Lync servers (Office 365) have started rejecting the RC4 stream cipher. Even though it breaks the SIPE plugin, this could be seen as an improvement as Microsoft has recommended to retire RC4 as used in their TLS implementations for years.

Check out the technical details on the SIPE bug tracker: Office365 rejects RC4 in TLS-DSK

Anyhow, the good news is that the SIPE developers have already implemented support for AES-128/256-CBC as mentioned in their changelog:

version 1.20.0 "???" (2015-XX-XX)
- Feature #82: Parse HTML from Lync conference URL (Stefan Becker)
- Feature #69: SRTP Support (Jakub Adam)
  * requires libpurple >= 3.0.0
- Fixed #285: Office365 rejects RC4 in TLS-DSK (Stefan Becker)
  * added support for AES-128/256-CBC

I’ve built the latest snapshot from git and can confirm that the plugin is working as expected on Slackware 14.1 64-bit. Huge thanks and kudos to the SIPE development team for their quick response.

If you cant wait for the next release, then roll your own by grabbing the source from http://repo.or.cz/w/siplcs.git?a=shortlog;h=mob

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