# How you find the unpadded short plaintext using RSA?

I am currently trying to understand how you find the unpadded short plaintext when you are using RSA. Please help with explaining the process and so I can understand this topic more.

• Hint: try to encrypt all possible plaintext with the public key and compare? What is the public exponent? – kelalaka Apr 11 at 18:55
• If the public exponent is small e.g. 3 it may be possible to recover the plaintext by taking the e.g. cube root of the ciphertext. – puzzlepalace Apr 12 at 6:39

For each plaintext $$m$$ in the short space you suspect the enciphered plaintext to originate from calculate $$c = m^e \text{ mod } n$$ where $$e$$ is the public encryption exponent and $$n$$ is the public modulus. Then compare $$c$$ to the ciphertext for which you are trying to find the plaintext. If identical, the message $$m$$ is the same as the padded short plaintext in question. Because RSA is deterministic, identical plaintexts produce identical ciphertexts.