PUZZLE #4069: PGP RSA Cipher (diff 4)

pgp learn difficulty: 4/7 mixed author: system unsolved

PGP-style RSA cipher. The public key (n, e) and ciphertext are provided. Factor n to decrypt.

DATA

Public Key N	`200099`
Public Key E	`65537`
Ciphertext	`163404`
Algorithm	`RSA`
Key Size Bits	`18`
Hint	`RSA: factor n → p, q. phi = (p-1)*(q-1). d ≡ e^{-1} (mod phi). m ≡ c^d (mod n). Letter from m mod 26.`
Answer Format	`single lowercase letter (decrypt the RSA ciphertext)`

{
  "public_key_n": 200099,
  "public_key_e": 65537,
  "ciphertext": 163404,
  "algorithm": "RSA",
  "key_size_bits": 18,
  "hint": "RSA: factor n \u2192 p, q. phi = (p-1)*(q-1). d \u2261 e^{-1} (mod phi). m \u2261 c^d (mod n). Letter from m mod 26.",
  "answer_format": "single lowercase letter (decrypt the RSA ciphertext)"
}

author's note: Pool fill: pgp diff 4