algorithm design - Why do we use multiple rounds of encryption ...
2018年1月4日 · Generally any cipher with rounds will have successful (if theoretical) attacks over a number of rounds. The problem is that you don't know which attacks will be devised in the future. So in the end some kind of margin is in order; there is a non-trivial balance between future proofing an algorithm and performance.
terminology - What are rounds in the context of ciphers?
2013年2月8日 · Many block ciphers are defined by specifying a round and then running that specification multiple times. For example, in AES, a round consists of the operations SubBytes, ShiftRows, MixColumns, AddRoundKey.
block cipher - How were the number of rounds for different key …
2012年5月21日 · Two rounds of Rijndael provide 'full diffusion' in the following sense: every state bit depends on all state bits two rounds ago, or a change in one state bit is likely to affect half of the state bits after two rounds. Adding four rounds can be seen as adding a 'full diffusion step' at the beginning and at the end of the cipher.
feistel cipher and number of rounds - Cryptography Stack Exchange
2018年10月2日 · In practice, cryptographers don't tend to design ciphers with a heavy PRF for the f-function but instead apply more rounds with a weaker f-function to get the requisite strength. For this reason, there is no typical or default choice for the number of rounds in a Fiestel cipher.
cryptanalysis - Rounds in cryptography - Cryptography Stack …
2014年11月30日 · Using only 4 rounds instead of 10 in AES-128 is broken, even without special prequesits. Breaking a few rounds of a cipher is normal, because the secure properties of an algorithm have to slowly establish through the rounds. If 9 out of 10 rounds would be broken, that would be much more alarming.
How to design number of rounds in my cipher?
2020年6月20日 · Every pair is key and define specific $2^{128}$-element permutation in my cipher. Now we can composite rounds. Let's do 21 rounds. So we need 21 keys from our 64-element collection. In the end our main KEY is 21-element variation with repetition. $64^{21}$ is about $2^{128}$. So we have good security level. But let's say we would like to do 5 ...
block cipher - How many rounds of encryption is ideal?
2018年10月9日 · How many rounds cannot really be answered as it depends on the design of a (block) cipher. As many as required to withstand attacks found by crypt-analysis, plus quite few more in case the attacks are enhanced is the best we can do. AES-128 has a mere 10 rounds, but those rounds are rather complex.
Symmetric cipher key size vs number of rounds. Longer key
2018年4月16日 · A common block cipher design goal is that it is as fast as possible while meeting its security level (matching its keysize per the previous goal). Increasing the number of rounds can make a cipher more secure, but does make it slower. Hence, for a cipher design meeting its security and speed design goals, more secure cipher more rounds.
Feistel cipher vs Substitution-permutation network - number of …
2015年12月20日 · The reason for this is pretty simple: the cipher designer already provided the *recommended * number of rounds and – if possible – related security proofs. The recommended number of rounds represents the (let’s just call it) “ideal” number of rounds in relation to the cipher’s security.
block cipher - Where would a "half round" come from?
2018年12月31日 · In the hierocrypt-L3 description, the cipher takes 6, 7, or 8 rounds. Example source code also seems to follow this same specification of 8 rounds for 256-bit keys. Wikipedia shows 8.5 rounds for 256-bits. I found it some other literature as …