Method for Testing and Hardening Software Applications

A method for testing a white-box implementation of a cryptographic algorithm, said implementation being executable on a processor, generating a ciphertext from a plaintext by means of a secret key and being present in the processor in the form of machine commands, wherein the processor comprises at least one register and the method comprises the following steps:

• (a) feeding one plaintext of a plurality of plaintexts to the white-box implementation;
• (b) reading out and storing the content of the at least one register of the processor stepwise while processing the machine commands of the white-box implementation stepwise, wherein intermediate results can be generated while processing the machine commands of the white-box implementation stepwise for generating the ciphertext from the plaintext;
• (c) repeating the hereinabove steps (a) and (b) with a further plaintext of the plurality of plaintexts N-times;
• and
• (d) statistically evaluating the contents of the registers and the plaintexts, the intermediate results and/or the ciphertexts generated from the plaintexts by searching for correlations between the contents of the registers and the plaintexts, the intermediate results and/or the ciphertexts generated from the plaintexts to establish the secret key.