New answers tagged integrity
If the plaintext format is indeed as you describe, then you're out of luck: the insertion of the newlines and the consequent shifting of the plaintext records is enough to disrupt any structure in the ciphertext. If the plaintext were longer, say, 8 records, then it could work, but with just 7 records there's no way to switch the first and last record ...
Well, DES is weak and since you can guess a plaintext you can use a rainbow table to crack the key and then of course decrypt and re-encrypt the message. Apart from that I don't think you can re-order the blocks to change the first and last line, if you really want to do this specific operation.
This procedure, also called signing a message, does not encrypt the message itself, thus does not ensure it cannot be read by others. Instead, a hash sum of the message is encrypted using the private key. For verifying, the recipient again calculates the hash sum of the message, and decrypts the hash sum calculated by the sender using the sender's public ...
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