3

in symetric encryption it is different. however in asymetirc encryption lets say we have a part of the cipher text only,not the entire ciphertext. you also have the private key. can you decypt that specific part of the cipher text with the private key

2 Answers2

1

Most practical asymmetric encryption uses symmetric encryption to encrypt the bulk of the data, so many of the same design principles and design considerations in symmetric encryption also applies to asymmetric encryption.

In most practical asymmetric encryption, the asymmetric encryption is used to encrypt a symmetric session key and to sign. As long as the partial ciphertext includes the header block where the session key is stored, you'd be able to decrypt partial asymmetric encryption if the underlying symmetric encryption can be decrypted with partial text. You'd most likely get a signature error, but this don't prevent the partial decryption itself.

If you're asking whether pure RSA or EC itself can be decrypted with partial text, as implemented in most practical encryption system, then no, as these asymmetric ciphers are used only to encrypt a single block (the symmetric session key), so no block chaining vulnerability would be possible.

Lie Ryan
  • 31,089
  • 6
  • 68
  • 93
  • So basically you mean it depends on algorithms –  Mar 27 '17 at 01:51
  • Does ssl also use symetric key session –  Mar 27 '17 at 01:55
  • @sweetpunk: yes. SSL/TLS uses either RSA or DH key exchange to negotiate the symmetric session key. The symmetric encryption itself usually uses AES or ChaCha20. In the past, some of the symmetric ciphers used were DES, 3DES, and RC4, before they were replaced with better options. – Lie Ryan Mar 27 '17 at 02:23
  • ok so during transmission of ciphertext is the header block transferred first or the rest of the ciphertext –  Mar 27 '17 at 02:24
  • You should read "[How does SSL/TLS work?](https://security.stackexchange.com/q/20803/2755)", which should answer your questions. If there's anything else you're still unsure about, you can then open another question and ask a more specific question. – Lie Ryan Mar 27 '17 at 02:30
0

Assuming you've used RSA as the encryption algorithm, the answer is "no", a partial decryption is not possible. Decrypting RSA involves performing math on the ciphertext. If any of the ciphertext is missing, the math won't work and there will be no recovery of the encrypted data.

John Deters
  • 33,650
  • 3
  • 57
  • 110