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4

So in what cases might we need only encryption but not decryption? It seems strange we would encrypt something that does not need decrypting at some point. For example, the CTR mode uses only Encryption, and CFB, OFB. It seems PRESENT can decrypt a ciphertext by running it in reverse. So why the need for some careful management for PRESENT to be ...


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When using lightweight ciphers, the block size can make a huge difference to security. Fortunately, there has been a lot of work in recent years on tight bounds for modes of operations, and methods for going beyond the birthday bound. These modes are not stated as being especially for lightweight ciphers, so don't search for that. However, there is no doubt ...


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I cannot find anything simple on time complexity for cryptographic components (functions?) as describable above You wont really find anything because those components are generally not described that way. There are simply too many ways of implementing each component in hardware and software on multiple platforms, and they do not always obey the rules of big-...


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Permutation layer diffuses the small changes globally(tries to spread over the complete block). If permutation is not well thought out, then diffusion may be weak and changes may not spread throughout the complete block. The cipher output may be treated as concatenation of output from multiple identical ciphers with smaller block length. For Example ...


2

I think that the reason for 31 rounds is in their paper, Section 5.1. Bogdanov et al. have approximated a small $2^{−43}$ bias that occurs after 28 rounds of linear analysis. Therefore they added another 3 rounds to arrive at a slightly unusual odd number of rounds. This is how ciphers are designed. There are no specific rules passed down through the ...


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There are many sources presenting the test vectors. But you can also extract it from sourcecode implementations as opencores.org et al offer them… Plaintext: 0000000000000000 Key: 00000000000000000000 (80-bit) Round key 1: 0000000000000000 Round key 2: c000000000000000 Round key 3: 5000180000000001 Round key 4: 60000a0003000001 Round key 5: ...


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to prevent self-similarity of key scheduling The importance of constant addition (not only present cipher) appears in preventing key schedule-based attacks such as slide attack ,related key attacks and other structural attacks such as: invariant subspace attack , and nonlinear invariant subspace attacks. paragraph 5.4 Key schedule attacks in original ...


2

A bona fide use case for encryption only is inside a true random number generator (TRNG). If you have something small like:- it's common to whiten the raw entropy signal using a cryptographic primitive. PRESENT could be used in some form of CFB mode, although there are examples of vanilla ECB mode being used. The designers of these simple key type TRNGs ...


2

Ciphers that are targeted for light-weight applications often have some common, but one-off, use cases. I have an IC with and ADC that is passively powered via RFID, and then sends encrypted data via SIMON. There's no commands required, so it is strictly one-way. I illuminate the IC electrically, and then it sends me a sample from the sensor. PRESENT is ...


2

You may need to specify your model of computation to make your question answerable. In some models bitwise XOR is ${\rm O}(n)$ in the number of bits being XORed; it others it can be ${\rm O}(1)$, because all those bits can be processed in parallel. In some models the answer can even depend on the relationship between the number of bits being XORed and the ...


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The avalanche effect is the property of a cryptographic primitive, whereby flipping a single input bit causes (on average) 50% of all of the output bits to flip. This can be simply accomplished by an S box. For the avalanche effect to occur, a simple randomly generated S box is all that is required. However for security purposes, a much cleverer design is ...


2

In short: Trace back where bits come from in every byte in the output state (8 bytes) of the SP_network. In one round, after we have xored the round key bits, we have 8 bytes (a 64 bit word, with rightmost byte 0, leftmost byte 7 etc. which in the linked software (which is byte oriented) is represented as state[0] to state[7]) are put nibblewise through ...


1

The test vectors for PRESENT cipher 128 bit key size are: $$ \begin{array}{c|c} \def\tabentry#1 {{\scriptstyle\mathtt{#1 }}} K & P & C \\ \hline \tabentry 0x00000000000000000000000000000000 & \tabentry 0x0000000000000000 & \tabentry 0x96db702a2e6900af \\ \tabentry 0xffffffffffffffffffffffffffffffff & \tabentry 0x0000000000000000 & \...


1

I assume a cipher has a total time complexity. Where can I find the time complexities of a given cipher, especially DES, PRESENT and AES? And is there available time complexities per round of these ciphers? I did not see, any DES, or similar cryptographic algorithm complexity in the literature. They are, usually, compared by the speed of their software ...


1

Question 1 In simple terms, how does the key schedule protect it from key related attacks? According to the paper "Lightweight Block Ciphers Revisited: Cryptanalysis of Reduced Round PRESENT and HIGHT", the non-linearity of the key schedule contributes to resistance to related key attacks: Related-key differential attacks, on the other hand, are ...


1

For your first question, there are two permutations in PRESENT that we could consider changing: The nonlinear layer, i.e. a parallel application of an S-box. The linear layer, which is a bitwise permutation. The statistical saturation attack is not really based on the properties of the S-box, so one might not expect that replacing it helps a lot. However, ...


1

Yes, you might think that the bits return to their original positions. But they don't because those aren't the bits you're looking for. They've changed. Specifically, you need to consider the effect of the s-boxes. If a single bit goes into a s-box, it's very nature means that on average, two bits come out. Similarly, if three bits go in, two bits still ...


1

In the original paper (pp. 16) one can find the requested test-vectors. The paper includes test vectors for all four cases you request (one or both of key and plaintext are $00...00$ or $FF...FF$). The following table shows the test vectors: Plaintext | Key | Ciphertext ------------------|------------------------|----------------- ...


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