PicoCTF_2017: ComputeRSA

Category: Cryptography Points: 50 Description:

RSA encryption/decryption is based on a formula that anyone can find and use, as long as they know the values to plug in. Given the encrypted number 150815, d = 1941, and N = 435979, what is the decrypted number?

Hint:

decrypted = (encrypted) ^ d mod N

Write-up

Math time! Since most calculators have a character limit, let's use a Python calculator!

>>> decrypt = (150815 ** 1941) % 435979
>>> print(decrypt)
133337

Therefore the flag is 133337.