Philipp Jovanovic

Practical Cryptanalysis of the Open Smart Grid Protocol

Philipp Jovanovic, Samuel Neves

Fast Software Encryption (FSE), 2015


This paper analyses the cryptography used in the Open Smart Grid Protocol (OSGP). The authenticated encryption (AE) scheme deployed by OSGP is a non-standard composition of RC4 and a homebrewed MAC, the “OMA digest”. We present several practical key-recovery attacks against the OMA digest. The first and basic variant can achieve this with a mere 13 queries to an OMA digest oracle and negligible time complexity. A more sophisticated version breaks the OMA digest with only 4 queries and a time complexity of about \( 2^{25} \) simple operations. A different approach only requires one arbitrary valid plaintext-tag pair, and recovers the key in an average of 144 message verification queries, or one ciphertext-tag pair and 168 ciphertext verification queries. Since the encryption key is derived from the key used by the OMA digest, our attacks break both confidentiality and authenticity of OSGP.