The researchers behind the security audit of the TrueCrypt disk-encryption software have completed their work and say they have found no evidence of any deliberate backdoors or serious design flaws in its code.

"Based on this audit, Truecrypt appears to be a relatively well-designed piece of crypto software," crypto boffin Matthew Green said in a blog post on Thursday.

The security community's attention became razor focused on the ongoing audit of TrueCrypt after the software's developers abandoned their work under mysterious circumstances last year. A message posted to TrueCrypt's official page urged users to uninstall it immediately "as it may contain unfixed security holes" and suggested Microsoft's BitLocker as an alternative.

This second phase of the audit examined TrueCrypt's random number generators and other cipher suites, following a first phase that reviewed the blueprints of the software. But although the auditors did find a few problems with TrueCrypt's code, they were minor and could only compromise security under very limited and specific circumstances.

For example, the Windows version of TrueCrypt relies on the Windows Crypto API, which can fail to initialize properly in some circumstances, allowing TrueCrypt to generate cryptographic keys based on predictable numbers, rather than random ones.

"This is not the end of the world, since the likelihood of such a failure is extremely low," Green observed. "But it's a bad design and should certainly be fixed in any TrueCrypt forks."

A number of such forks are already under development using the original TrueCrypt code as reference, among them CipherShed and VeraCrypt. The apparent lack of any serious security flaws in TrueCrypt, however, leaves open the question of why the TrueCrypt developers chose to close up shop to begin with.

One theory is that the cryptic message posted to the software's homepage was meant as a kind of "warrant canary" designed to warn users that pressure from one or more governments had made ongoing development of the software difficult or impossible. If true, that could have ominous implications for any future TrueCrypt derivatives.

"The loss of TrueCrypt's developers is keenly felt by a number of people who rely on full disk encryption to protect their data," Green wrote. "With luck, the code will be carried on by others. We're hopeful that this review will provide some additional confidence in the code they're starting with."

The full findings of the TrueCrypt security audit are available as a PDF, here. ®