Posted by Alex Klyubin, Android Security Engineer

The Android security team has been investigating the root cause of the compromise of a bitcoin transaction that led to the update of multiple Bitcoin applications on August 11.

We have now determined that applications which use the Java Cryptography Architecture (JCA) for key generation, signing, or random number generation may not receive cryptographically strong values on Android devices due to improper initialization of the underlying PRNG. Applications that directly invoke the system-provided OpenSSL PRNG without explicit initialization on Android are also affected. Applications that establish TLS/SSL connections using the HttpClient and classes are not affected as those classes do seed the OpenSSL PRNG with values from /dev/urandom.

Developers who use JCA for key generation, signing or random number generation should update their applications to explicitly initialize the PRNG with entropy from /dev/urandom or /dev/random. A suggested implementation is provided at the end of this blog post. Also, developers should evaluate whether to regenerate cryptographic keys or other random values previously generated using JCA APIs such as SecureRandom, KeyGenerator, KeyPairGenerator, KeyAgreement, and Signature.

In addition to this developer recommendation, Android has developed patches that ensure that Android’s OpenSSL PRNG is initialized correctly. Those patches have been provided to OHA partners.

We would like to thank Soo Hyeon Kim, Daewan Han of ETRI and Dong Hoon Lee of Korea University who notified Google about the improper initialization of OpenSSL PRNG.

Update: the original code sample below crashed on a small fraction of Android devices due to /dev/urandom not being writable. We have now updated the code sample to handle this case gracefully.

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See the article here:

Some SecureRandom Thoughts