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I'm quickly assuming your question asks how to retrieve the public (RSA-) key from a set of samples of unencrypted and encrypted messages. If you're question is about: "How can I get my files back after being infected by CryptoWall?" I suggest you read the hits by the search function on InfoSec. Please also note that in most use cases RSA isn't used to ...


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There's nothing wrong with using CTR mode to encrypt files, or anything else, as long as you make sure to use every nonce value only once. (And add authentication, if malleability would be a problem.) You could, for example, rewrite the whole file encrypting it with a new random nonce every time it's modified. Since you are assuming nonce reuse, an attack ...


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Some information about the RSA public key is revealed by the ciphertext. This is due to the fact that the ciphertext is a value between 1 and the modulus. Beyond this, I don't know what is revealed. However, what I can prove is that whatever you can learn from the plaintext and ciphertext together, you can learn from the ciphertext only. I can prove this ...


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No, if the RSA cryptosystem is secure, i.e. when it uses random padding such as PKCS#1 v1.5 padding or OAEP, then you cannot. As Stephen already mused, it is pretty likely that you can find out the key simply because it is included or can be derived; generally public keys are not meant to be secure. If textbook (raw modular exponentiation) RSA is used then ...


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The ciphertext should look like a random element within 1 and the modulus (since it is a value from within that range as Yehuda Lindell pointed out). Without knowing the modulus it should not be feasible to distinguish two ciphertexts encrypted with different keys. If the public key is stored in some key-database you could ofc try to encrypt the decrypted ...



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