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 Curious
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Apr
22
comment Multiple AES/ECB encryptions of different data with same key all end with same pattern
See: crypto.stackexchange.com/questions/20941/…
Apr
22
reviewed Approve Multiple AES/ECB encryptions of different data with same key all end with same pattern
Apr
22
reviewed Reviewed How does a certificate authority issue a digital certificate?
Apr
22
revised How does a certificate authority issue a digital certificate?
misc. grammar and spelling copyedits
Apr
22
reviewed Reviewed What is the “compression function” in Merkle-Damgård?
Apr
22
reviewed Reviewed Why isn't CTR mode (counter mode) used more often?
Apr
22
reviewed Reviewed Why isn't CTR mode (counter mode) used more often?
Apr
19
awarded  Curious
Apr
18
comment Is MCrypt's 8-bit OFB mode secure?
That's a good point, and I'd be grateful for any references to actual peer-reviewed articles proving (or disproving!) this claim. As far as I can tell myself, the proofs by Wooding do look reasonable at a glance, but I must admit that I didn't go over them in full detail, and they do involve a bunch of subtle details and corner cases one could easily stub one's toe against. Hence why I haven't accepted my own answer yet.
Apr
18
asked Is MCrypt's 8-bit OFB mode secure?
Apr
18
answered Is MCrypt's 8-bit OFB mode secure?
Apr
16
comment AES plaintext is smaller than 128 bits - how to expand?
Also note that key expansion does not actually mean what you seem to think it means.
Apr
15
reviewed Reviewed Difference between IPSEC SA and CHILD SA
Apr
15
reviewed Reviewed Website Certificate with different public key
Apr
15
comment why are both ipad and opad required for HMAC?
We could always replace one of the constants with 0, and the other with ipad ⊕ opad; all this would do is permute the keyspace.
Apr
14
comment RFID Protocol Cryptanalysis
After your edit, it's no longer clear what the actual scheme you're asking about is. You should either revert your question to its original state, or rewrite it to clearly describe the one specific scheme (or family of schemes) that you're interested in analyzing. If you wish to ask about a family of schemes, please try to limit the variation as much as possible, preferably to a small finite number of variants and/or a few adjustable numeric parameters like key length. Do not include parameters like "where $F$ is any function"; nobody can analyze a scheme at that level of generality.
Apr
14
comment RFID Protocol Cryptanalysis
XORing all the keys actually makes is worse: as soon as an attacker intercepts one $(k_i,r_i)$ pair, they can compute $k_{i+1} = k_i \oplus r_i$ and so impersonate the tag as many times as they want. Edit: The same holds also for $k_{i+1} = F(k_i)$, if anybody can compute $F$. If $F$ is secret (say, encryption with a secret key) then the first attack I describe won't apply, but the second may.
Apr
14
comment Are there equivalent IVs in DES/CBC?
If the key and the ciphertext are fixed, then no. If $P_1 = IV_1 \oplus D_K(C)$ and $P_2 = IV_2 \oplus D_K(C)$, then $P_1 \oplus P_2 = IV_1 \oplus D_K(C) \oplus IV_2 \oplus D_K(C) = IV_1 \oplus IV_2$. Thus, $P_1 = P_2$ if and only if $IV_1 = IV_2$.
Apr
14
reviewed No Action Needed Are there equivalent IVs in DES/CBC?
Apr
14
revised Are there equivalent IVs in DES/CBC?
added 899 characters in body