The invention discloses a log encryption method and device and a log decryption method and device, and the log encryption method comprises the steps of obtaining a plaintext log and a secret key; converting the plaintext log into an intermediate ciphertext, and converting the key into a key ciphertext; and encrypting the intermediate ciphertext by using the key ciphertext, so that the problem thatin the prior art, a log encryption method is lower in safety, is solved.