Researchers have found a new a new attack vector for TLS 1.1 and 1.2 protocol implementations, which wolfSSL has promptly fixed in its leading embedded TLS product with release 2.5.0 of the wolfSSL (formerly CyaSSL) library (https://www.wolfssl.com/wolfSSL/downloa … adForm.php).

In the paper "Lucky Thirteen: Breaking the TLS and DTLS Record Protocols" authors Nadhem AlFardan and Kenneth Paterson present a family of attacks that apply to CBC-mode for TLS (1.1 and 1.2) and DTLS (1.0 and 1.2). All of the attacks are based on a delicate timing analysis of the decryption processing needed in block mode. The various attacks are distinguishing, partial plaintext recovery, and full plaintext recovery in nature. All the attacks exploit the protocol when badly formatted padding is handled during processing. A MAC verification must still be performed on something to prevent existing timing attacks. The RFCs suggest using a zero-length pad which was thought to be safe, but these attacks show that it can be exploited.

There are a few ways to avoid the attack. Using stream ciphers is the simplest. Stream ciphers like ARC4, HC- 128, and RABBIT are not vulnerable because they don't use block mode and padding. HC-128 and RABBIT are unique to wolfSSL and also have the benefit of being extremely fast. Another way is to use Authenticated Encryption like AES-GCM and AES-CCM instead of block mode with CBC. wolfSSL includes several cipher suites utilizing Authenticated Encryption algorithms. Lastly, wolfSSL implemented the countermeasures suggested in the paper in version 2.5.0 to avoid timing attacks.

Founded in 2004, wolfSSL offers open-source, embedded security solutions that are fast, small, portable and standard compliant including wolfSSL, the C-language SSL library for embedded and RTOS environments; yaSSL, the embedded C++ SSL library; and yaSSL Embedded Web Server, a fast, embeddable, secure web server. Dual licensed, wolfSSL caters to the security applications in industrial automation, smart energy, surveillance, medical, military, telecommunications markets and the open-source community. Distributed worldwide, wolfSSL is headquartered in Bozeman, Montana.

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