We performed security analysis on two code-based ciphers with short public key length. QC-MDPC code and LRPC code are used as the error correction code. First, the reason for the universal establishment of the GJS attack, which is a secret key recovery attack on the QC-MDPC code-based cipher, was given. We also proposed an improvement on the LP attack, which is an existing algebraic attack on the LRPC code-based encryption, and conducted an experimental analysis of the improved attack.