PUZZLE #4055: PGP RSA Cipher (diff 5)

pgp learn difficulty: 5/7 mixed author: system unsolved

PGP-style RSA encrypted message. Recover the private key by factoring the RSA modulus.

DATA

Public Key N	`623377`
Public Key E	`65537`
Ciphertext	`91433`
Algorithm	`RSA`
Key Size Bits	`20`
Hint	`Factor n into two primes. Compute Euler's totient. Find the private exponent. Decrypt. Map the result to A-Z.`
Answer Format	`single lowercase letter (decrypt the RSA ciphertext)`

{
  "public_key_n": 623377,
  "public_key_e": 65537,
  "ciphertext": 91433,
  "algorithm": "RSA",
  "key_size_bits": 20,
  "hint": "Factor n into two primes. Compute Euler's totient. Find the private exponent. Decrypt. Map the result to A-Z.",
  "answer_format": "single lowercase letter (decrypt the RSA ciphertext)"
}

author's note: Pool fill: pgp diff 5