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I have an application that needs to combine two cascaded (symmetric) encryption keys using the Pohlig-Hellman cipher.

For example:

The system needs two keys for encryption $c = E_a(E_b(x))$ while it only needs one key for decryption $D_{a\otimes b}(c)=x$. The system may NOT need to consider Known Plaintext Attack or Chosen-plaintext Attack because the key is only used once.

Is it possible that the PH-based method can support encrypting large blocks? For example, can it support 1GB file encryption?

I am quite new to this area. Very much appreciated it if you could provide any tutorials on this.

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    $\begingroup$ It's usually recommended to avoid the Pohlig-Hellman cipher. Is there a reason why you specifically need this? $\endgroup$ Apr 29, 2020 at 11:36
  • $\begingroup$ I need to merge two cascaded keys (for encryption) into a single one (for decryption) thus to prevent the leakage of the two cascaded keys. $\endgroup$
    – Yuhang Ye
    Apr 29, 2020 at 13:40
  • $\begingroup$ @YuhangYe cascading is not secure Is the encryption more secure if we apply Pohlig-Hellman cipher twice with different keys but with the same modulus?. $\endgroup$
    – kelalaka
    Apr 29, 2020 at 15:00
  • $\begingroup$ @kelalaka In my application senario, I do not need to worry about KPA or CPA. The key is only used once then it will be disposed. $\endgroup$
    – Yuhang Ye
    Apr 29, 2020 at 15:26
  • $\begingroup$ @YuhangYe For Pohlig-Hellman Cipher double encryption is equal to single encryption so that it doesn't increase the key size. Why not AES, ChaCha20, etc? $\endgroup$
    – kelalaka
    Apr 29, 2020 at 15:51

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