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location Kiev, Ukraine
age 24
visits member for 1 year, 10 months
seen Jan 2 '13 at 7:09

C++ Programmer in cryptology scope.


Dec
3
comment Ensuring integrity of a client side script
Do you assume attacker is on channel or a client can be attacker too? In first case you can use something like SSL to protect the channel.
Nov
24
comment Should we sign-then-encrypt, or encrypt-then-sign?
@Ricky Demer: signature will be correct only if all decrypted text including padding is identical to the sender's source. So, attacker will take message "Signature is correct" in 2 cases: 1) he pass the message unchanged. 2) He changes ciphertext in some way so the decrypted text is the same as in correct message. The only way to do that is re-encrypting entire message with different IV. I don't think it's possible without knowing the key.
Nov
23
comment Should we sign-then-encrypt, or encrypt-then-sign?
Ok, now I finally understood what did you mean. No, recipient is not a padding oracle. he just says "Signature is correct" or "Error". No information of correct or incorrect decryption. Even if attacker can modify ciphertext to be decrypted to the same plaintext, he cannot get any block of this plaintext.
Nov
23
awarded  Commentator
Nov
23
comment Should we sign-then-encrypt, or encrypt-then-sign?
Ok, I'll ask another way: what property of transferred information can be broken? Confidence, integrity, authenticity or what else?
Nov
23
comment Should we sign-then-encrypt, or encrypt-then-sign?
So, what is the problem in this case? If recipient get a correct plaintext, no matter how it was derived.
Nov
23
comment Should we sign-then-encrypt, or encrypt-then-sign?
If attacker change the ciphertext somehow, the decrypted text will be changed too and signature verification will fail.
Nov
23
comment Should we sign-then-encrypt, or encrypt-then-sign?
@Ricky Demer: How can attacker get a plain text? There are no conditions for chosen ciphertext model.
Nov
23
comment detecting ROT13/base64 encryption
Both of them are encoding methods. Not an encryption.
Nov
23
comment Encrypting with private key in Public Key InfraStructure
You are doing it wrong. Encryption of hash with RSA private key is called signing. Note, that RSA is one of the few ciphers that provide signature as encryption with private key. The goal of second operation is not clear. Why you encrypt a symmetric key? I see you need classic sign-then-encrypt scheme.
Nov
23
answered Should we sign-then-encrypt, or encrypt-then-sign?
Nov
19
comment Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
That's not the same. MAC is based on secret key and cannot compromise sigher's identity.
Nov
19
comment Is this how padding can work?
Padding is applied to plaintext, not ciphertext.
Nov
19
comment Is it safer to encrypt twice with RSA?
It will be impossible with padding due to encrypted message size.
Nov
19
awarded  Teacher
Nov
19
answered Is it safer to encrypt twice with RSA?
Nov
19
comment Is this how padding can work?
So, what is the problem? Last byte will contain the block length, so you will know that entire last block is a padding.
Nov
19
answered Is there an authenticated encryption scheme where the recipient can attribute the message to a single sender?
Nov
19
awarded  Supporter