# Tag Info

80

It (or rather, the software running on it) will use arbitrary-precision ("bignum") arithmetic. The way this works is basically the same way in which you (probably) learned to do arithmetic on paper at school. The arithmetic taught to us humans at school is base-10 arithmetic — that is, we represent numbers as strings made up of ten different digits, ...

16

Contrary to the other answer, I'll be assuming the hash function is of the password-oriented kind; and my answer will be: input size has almost no influence on speed in good practice, even for much longer input than in the question. Password-oriented (or entropy-stretching, key-stretching) hash functions are, for example, suitable to transform a (password, ...

13

I believe that it is for two reasons: Nontable based implementations of AES are possible, but (assuming you don't have AES-NI or something similar) are significantly slower than table based implementations (perhaps $10\times$ to $20\times$ slower) For a lot of uses, timing attacks aren't particularly relevant (as either the attacker can't get the start/...

11

Bitslicing is a technique where a computation is Reduced to elementary operations (called gates) with two bit inputs (typically NOR, XOR, and similar like OR AND NAND NXOR), rather than operations on words or integers spanning several bits. Executed in parallel, with as many simultaneous instances (on a single CPU) as there are bits in some register kind, ...

9

If I understand your question correctly, you are essentially asking if points in Edwards and Montgomery curves can be represented in Weierstrass coordinates. This is true; in fact, any elliptic curve over a prime field can be represented in Weierstrass form $\mathcal{E}_{w}^{a, b} : y^2 = x^3 + ax + b$, and by extension its points can too. The question, ...

9

What makes crypto code vulnerable to timing attacks is data dependent timing variations. Branching according to a round counter, or to the key size, does not create a vulnerability. Most implementations of AES make no branch according to key or data value, and supressing other branches won't help. The main source of data-dependent timing variations in AES ...

8

The basic idea of bitslicing, or SIMD within a register, involves two parts: expressing the cipher in terms of single-bit logical operations (AND, OR, XOR, NOT, etc.), as if you were implementing it in hardware, and carrying out those operations for multiple instances of the cipher in parallel, using bitwise operations on a CPU. That is, in a bitsliced ...

8

I finally untangled what this code is doing. YES. The quick version of why this is true is that the first 128 bits of entropy which the system collects get mixed directly into the nonblocking pool, bypassing the input pool. The logic which implements this is part of each of the add_foo_randomness() functions: r = nonblocking_pool.initialized ? &...

7

I've checked out the source code (well, more or less, it's not that well designed, the main crypto class is 1600 lines) and as Richie guessed, the algorithm is stored together with the ciphertext. Pretty gruesome stuff, but it does do EAX mode for text strings to my surprise. It probably only uses it for text strings originating from the password vault code ...

7

All hashes I know of are block oriented. The time required to calculate the hash scales with the number of blocks to be hashed. There is a small constant overhead dealing with the IV and, possibly, a finalization function.

7

Of course the processor cannot process such large numbers directly; this is done though a library such as GMP. See Wikipedia for a list of such libraries, and a good textbook such as that of Gerhard and von zur Gathen for the underlying ideas. The freely available Handbook of Applied Cryptography also talks about this, especially in Chapter 14.

7

This is identical with CTR mode encryption with a MAC. That's known to be secure. It doesn't say in your question if: the Ai blocks are completely unique; the header is included in the MIC calculation. If those preconditions are met then I don't see any issue with the protocol. The first one I cannot verify but seems likely, the second one is certainly ...

6

As pointed by CodesInChaos, you'll need to know the padding used; depending on application that could be RSASSA-PKCS1-V1_5, or RSASSA-PSS, or some of the three schemes of ISO/IEC 9796-2, etc.. Hashing, and padding check, are a significant part of the code. In any case, yes, it is possible to implement RSA-2048 signature verification on a Cortex-M0 ...

6

An initialization vector is, in fact, always binary. It's just random bits. So, if you choose to encode those bits as a hexadecimal string for ease of storage or transportation, that is fine. However, since it is the binary that is the IV, you will need to decode it back from hexadecimal to a binary value before using it in the decryption process. As a ...

6

Well, the obvious thing to do is give it a long list of integers of known primality, and see whether the algorithm reports it correctly (with it occasionally reporting a composite as "relatively-prime" not being counted as an error, as long as it reports that value as composite at least 75% of the time). However, that simple-minded test might miss something....

6

At least for compiled languages it should also be possible to have tools that perform static analysis on machine code, shouldn't it? Indeed, such tools exist. There are companies specialized in this domain which provide this kind of tools (see this datasheet for example). But you should note that an only software tool will not be able to detect all ...

5

So how secure can non-assembly code truly ever be against timing attacks? First of all, let me state that this is a tricky subject. The simplest method is of course to do away with the lookup tables or and other components that are vulnerable to timing attacks. So when a cipher designed, it should require a minimum of vulnerable components. And during ...

5

Bitslicing is a technique that allows multiple instructions/Data points to be encoded into a single register. The idea is that you encode several bitwise operations within a single register. So, instead of 32 bitwise OR operations in sequence, you could reduce the total number of operations by cramming the data into SIMD registers and executing in ...

5

There are typically four different settings where you want to run your crypto. The Central Processing Unit (CPU). This may be a classic desktop or laptop CPU or the one of your embedded device. Its characteristic is that it usually has rather few computation cores ( < 20), but it can use the ones it has very fast and can execute arbitrary instructions (...

5

I'll assume the question really is: when I perform low-order-bit steganography on an uncompressed image (inserting 6 bits encoding a character into the low-order bit of 6 bytes coding the R, G and B channels of 2 pixels), I find that compressing the resulting image gives a bigger file than compressing the original image for a given setting of the program ...

5

The obvious answer to your question is "yes". The kernel mode implementation pointed to by otus clearly shows that it can be done. That it can be done doesn't mean it gets done however. Many Google searches for sourcecode don't show any OpenSSL code that implements this functionality. In general, OpenSSL doesn't rely on the crypto code of the kernel. So, ...

5

This is a good question, but I would consider hardcoding a known good group. There does not seem to be an advantage to letting the server decide if you can afford to use high enough parameter values. The SRP paper lists the following checks: "n is a large safe prime" (this is your first three points) "g is a primitive root of GF(n)" (your next point) "A >...

4

You can use any library you like, as long as it is has been tested for the specific algorithm. In other words, if $G^x$ is implemented in a specific library you must make sure that there are unit tests and if it is used in a verified algorithm. There are some hints you can take from the library to see if it was programmed well: the code should point to ...

4

All internal operations of a perfectly standard-conforming AES implementation can be conveniently implemented over bytes, without carry propagation. There's no security flaw implied. The worst that's bound to happen is that for some operations (like XOR with a 128-bit, 16-byte subkey), things must be repeated over several bytes, and a wider word would reduce ...

4

I think the flash implementation is wrong: (using Linux, OS X terminal etc.) not true, see below echo 328831e0435a3137f6309807a88da234 | xxd -r -p > plain.dat openssl enc -e -aes-128-ecb -iv 00 -K 2b28ab097eaef7cf15d2154f16a6883c -in plain.dat -out plain.dat.out -nopad yields hd plain.dat.out 00000000 57 16 aa fa ...

4

Triple DES is a block cipher. (Specifically, it's a variant of the old DES block cipher with better security, but several times lower performance.) You can use it to encrypt small blocks of data (64 bits = 8 bytes, for Triple DES), but what it's really useful for is as a building block for other cryptographic schemes, such as stream encryption or message ...

4

What you are looking for is a definition of PEM, privacy enhanced mail. Obviously PEM is not just used for mail anymore. The definition of the header lines seems to be best described by section 4.6: "Summary of Encapsulated Header Fields" of RFC 1421: "Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures"....

4

The answer is simple. AES is in itself a pseudorandom function, so an output from a single block encryption will produce 128-bits of pseudorandom numbers. Now to use AES to generate longer sequences, you will have to use a block-cipher mode that lets you do the same. Here is a small list of a few very popular modes ment for PRNGs: Counter(CTR): Counter ...

4

Does such an entity exist? No, not really. There isn't any organizations who's in the business of doing public cryptanalysis, and there certainly aren't any organizations that are sufficiently trusted for the cryptographical community to say "we know algorithm X is secure - organization Y said so". Let's go through the likely suspects: NSA (and other ...

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