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Jan
30
answered Is there a reference that prove that the AES Key Schedule generate random looking round keys?
Jan
30
reviewed No Action Needed How secure is it to use password as AES key?
Jan
30
reviewed Close Achieving 32-bit verification code with 16-bit CRC?
Jan
30
reviewed Close How are calculated numbers in AES S-box?
Jan
30
reviewed Leave Open 1 Billion Bit Encryption?
Jan
29
comment In RSA, why does $p$ have to be bigger than $q$ where $n=p \times q$?
The question was based on behavior seen within OpenSSL; the OpenSSL bignum library handles negative numbers properly, and hence this answer is irrelevant in the context of the original question.
Jan
29
reviewed No Action Needed How do I communicate the value of the initialization vector to the end user? Should it be part of the encrypted message?
Jan
28
reviewed Reviewed Point decompression on an elliptic curve
Jan
28
comment Point decompression on an elliptic curve
Shanks-Tonelli is the general answer for prime curves; however most elliptic curves have $p \equiv 3 mod 4$, and in this case, the problem can be simplified: to compute the square root of $n$, you just compute $n^{(p+1)/4}$ (and check that that value squared gives you $n$; this last bit catches values of $n$ that don't have a square root)
Jan
28
reviewed Close Is there a strong cryptographic reason for GCM's 2^39 - 256 bit limit?
Jan
28
reviewed No Action Needed Why isn't CTR mode (counter mode) used more often?
Jan
27
comment Proving that an encryption scheme is susceptible to certain attacks
@user21547: if $e_1 - e_2 = a(m_1 - m_2) + (k_1-k_2)p$ and $e_2 - e_3 = a(m_2 - m_3) + (k_2-k_3)p$, what is $(e_1-e_2)(m_2-m_3) - (e_2-e_3)(m_1-m_2)$?
Jan
27
comment Proving that an encryption scheme is susceptible to certain attacks
@user21547: oops, I meant them as arbitrary parameters -- I forgot that the cipher used them as key variables. I changed the answer to use the values $x, y, z, w$
Jan
27
revised Proving that an encryption scheme is susceptible to certain attacks
edited body
Jan
27
comment Is signing a message just encrypting it with private key?
Also, if you're not talking about RSA, but instead talking about, say, DSS or ECDSA, 'signing by encrypting' is not at all accurate, even as an oversimplification.
Jan
27
comment Is there a strong cryptographic reason for GCM's 2^39 - 256 bit limit?
@Jeff: the security proof for GCM states that if you have a valid $N$ block encrypted message, any change to the message (made by someone who doesn't know the AES key) would authenticate with probability at most $(N+2) 2^{-128}$. By allowing large values of $N$ (by allowing long messages), this significantly reduces the integrity guarantees of GCM
Jan
27
reviewed No Action Needed Is there a strong cryptographic reason for GCM's 2^39 - 256 bit limit?
Jan
27
reviewed No Action Needed In ECC, how do I prove that point addition is commutative?
Jan
27
reviewed No Action Needed Why can't you just clone encrypted data and use it?
Jan
26
revised Proving that an encryption scheme is susceptible to certain attacks
Hmmmm, looking at it again, I suspect you might need three chosen plaintexts for the third scheme