Resumen
In 2001, a CFS signature scheme based on the Niederreiter cryptosystem was proposed. The signature algorithm is based on code cryptography, which makes the signature resistant to post-quantum attacks. However, there are certain difficulties in its implementation. One of them lies in the complexity of constructing a signature due to the low probability of receiving an acceptable syndrome that can be easily decoded. This article considers a known way of modifying the original signature scheme to solve this problem. The paper studies the use of a code hash function to quickly obtain a decodable syndrome. When considering the compression function of the hash function, an error was found in its construction and the insecurity of the signature scheme built on such a hash function was proved.