0

I'm taking this new cryprography class and i'm kinda stuck. here is the problem:

"You know that the word “good” (let’s say message m), consisting of 4 characters, has been encrypted, through the OTP, into a known ciphertext c1. You don’t know though the secret key k. The sender of the message re-uses the same key k to encrypt another message (let’ say m1) and computes a known ciphertext c2. Show that you can find out the unknown message m1."

Any suggestions? Thank you in advance.

Artjom B.
  • 61,146
  • 24
  • 125
  • 222
user15594577
  • 1
  • 1
    Search for "two time pad" (which is the name of this mistake). https://crypto.stackexchange.com/search?q=two+time+pad – Rob Napier Apr 09 '21 at 20:56
  • 1
    Isn't clear `(m xor key = c` ), since you know, `m` and `c1` you know ... – kelalaka Apr 09 '21 at 22:36
  • `m XOR key = c` and `m1 XOR key = c1`. If you XOR these two together you get `m XOR m1 = c XOR c1`. You know m, c, and c1. Solve for m1. – rossum Apr 11 '21 at 10:24

0 Answers0