# Annotated Posts

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### Are Bitcoin's blocks signed by the miner? [migrated]

To my understanding, at no point in the Bitcoin Whitepaper does it say that blocks are signed by the miner. However, one could see the advantage of having blocks signed. Thus I wonder if in the ...
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### How to pass the output of a function to itself a number of times in RNG? [migrated]

I'm trying to pass the output of a function in C to itself a number of times but I'm still getting the same answer each time (I tried to pass it by value and by reference I do not know which is the ...
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### Cross Platform ECDH encryption and Decryption Java and c# [migrated]

I am not expert in encryption. We have requirement to encrypt the data in c# and decrypt the same in java. We were able to encrypt and decrypt the data for same key in c# and java. When we try to ...
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### Can Big Data attack RSA by just calculating many prime multiplications in advance? [duplicate]

Intro I am somewhat new to cryptography. Repeating the basics of RSA from How are the primes used to generate RSA keys?: Textbooks say the one-way function is merely two primes (with some critical ...
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### Decrypt message in swift encrypted in java using AES/GCM/NoPadding [migrated]

I want to create secretKey(symmetricKey) using my EC privateKey and publicKey from backend(Java) and decrypt message using that secretKey. How to achieve this? Here is implementation: This is how ...
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### What kind of random algorithm is used in this game? [migrated]

I am playing a game for iOS that uses a deck of 48 cards and I would like to reverse engineer the kind of algorithm that is used to generate the random deck of cards such that I can predict which card ...
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### How to implement AES in crypto++ which is applied multiple times to an input? which AES mode? [migrated]

For my target application I want to use AES multiple times in a row for a given input. After encrypting it $i$ times in a row it should result in same starting input if decrypting it $i$ times ...
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### Does it increase security if the CBC chunks of a AES-256 encrypted bytestream are uploaded to different clouds? [duplicate]

I want to backup my data according to the 3-2-1 rule. I already backup to 2 different drives (2 different systems) at home. In addition i would like to use cloud storage (Google, Amazon etc.). ...
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This is a soft question regarding comparisons between government security services (eg, NSA or GCHQ) and open-source research (e.g., academia). Hopefully it's on-topic for this site! In essence, my ...
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### Factorization of a number obtained by a modular multiplication operation can reveal factors of the used operands? [duplicate]

Consider a number $r$ obtained by: $r=a \cdot b \mod n$ Can knowing the factorization of $r$ reveal some information (bits) of $a$ and $b$ ?
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### What's the issue with Apple's backdoor?

I was reading Apple's public letter here regarding the "backdoor" that they have been asked to create. I'm very unclear exactly what the issue is. There was no backdoor in the encryption algorithm ...
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### Does there exist a hash function which has a fixed point? [duplicate]

Does there exist a hash function $h$ and an input $x$ such that $h(x) = x$? I believe this is a special case of collision-resistance. I imagine such a case is guaranteed not to be possible (otherwise ...
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### How to determine the next number from java's Random method [closed]

I understand a little how Java's Random class works. I have two random numbers output from calls to nextInt() from a ...
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### Can error correction and detection be done without adding extra bits?

I have gone through error detection and correction techniques like Hamming codes, and BCH codes require extra parity bits for detection and correction. While sending data, we always seem to introduce ...
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### Apple CryptoKit - Understanding its portability

I've been playing with Apple's CryptoKit (their effort to make their old CommonCrypto lib more modern and easy to use via Swift, their programming language). I'm interested to see how portable it is.....
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### DES/CBC : incorrect first 8 bytes [duplicate]

Question about DES-CBC : how to know IV if I have key, input buffer (plaintext), output buffer (encrypted) and decrypted result where first 8 bytes are incorrect but all other bytes are correct ?"
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### Does encrypting the key with itself make it easier to crack the ciphertext? [duplicate]

As the title states; Is there any risk from encrypting the key with itself? EG. $C = AES(K=K, M=K)$ I'd assume not; after all, how does having the key for a safe inside the safe make it easier to ...
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### Why is “mod(n)” so central to most aspects of cryptography? [duplicate]

When I first started learning cryptography, I had my first a-ha moment when I fully appreciated the value of a One Time Pad and XOR and all the functions that attempt to emulate that OTP's randomness (...
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### What's the difference between a Key Derivation Function and a Password-Hash? [duplicate]

It seems to me that anything that was sufficiently good as a KDF would work just fine as a password hash, though the reverse might not be true. Are there considerations specific to password-hashing ...
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We don't.${}{}{}{}{}{}{}{}{}{}$ Moderator note: This answer exists for historical significance, but it does not meet the guidelines for answering questions, so please do not use it as evidence that you can post similar answers here. This answer and its comments are frozen and cannot be changed. More info: meta.

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### Symmetric encryption mode where ciphertext size is plain text size [duplicate]

I've had many questions on Stackoverflow on how to minimize the output of a cipher - during encryption of course - to the same size as the input. Obviously this is possible for a single block of ...
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### What is the current time limit of Keccak inversion? [closed]

All sub-functions are referenced with respect to Keccak. It’s my understanding that the sub-function theta() would result in the largest resource allocation when attempting to invert Keccak. If this ...
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The advantages and properties exhibited by XOR are also exhibited by XNOR, like the ones mentioned in many answers like this one Information is preserved. $c = a \oplus b$. One may recover $a = c \... 1answer 546 views ### 2-round generalized Feistel network Write the decryption of a 2-round generalized Feistel network given below.$P_i$denotes plaintext blocks of each 32-bits.$RK_i$denotes the round keys.$WK_i$denotes 32-bit keys applied ... 0answers 422 views ### Misunderstanding Broadcast Encryption [duplicate] I have a secret message which I want to encrypt such that any of several different keys can open it independently. The keys can't know about each other and it has to be able to work completely ... 2answers 320 views ### Are there any tools for expressing the cipher operations as a system of equations? The first step In Algebraic-attack is expressing the cipher operations as a system of equations. Is there an automated tool to do this? 0answers 1k views ### What happens if a Sha 256 input is too long? [duplicate] Doesn't SHA-256 only take up to 512 bits for the input block? What happens if the input is really long? 0answers 156 views ### discrete logarithm vs normal logarithm [duplicate] Crypto schemes normally use discrete logarithm instead of normal logarithm. I think this has to do with the fact that discrete logarithm is hard to solve while normal logarithm isn't. Can someone ... 2answers 2k views ### Is this a correctly formatted PGP session key packet? RFC 4880 may be full of information, but it can be incredibly vague at times, so im looking for someone who actually knows the answer to this. Given this public key: ... 2answers 3k views ### suggestions for cryptography projects for an ece 3rd year student I am an electronics and communication engg student currently doing my 3rd year second semester. i am interested in info coding and the security aspects of it. As an ECE student i want to know what is ... 5answers 11k views ### How secure is a client-side javascript encrypter? A friend of mine needed help with her website and asked how to send me her login information securely. I've never known how to do this, so I figured now was the time to learn. After some googling, I ... 3answers 5k views ### Is cryptography an interesting field for research? I am now styding for first year bachelor's degree in Mathematics for IT. In the future I would like to major in the same field and possibly continue trying to get a Ph.D. But I still have options to ... 1answer 2k views ### Verification of identity by certification authority I have question about how a user's identity is verified by a Certification Authority. As I understand it, the process works as follows: User generates his private key and (with the help of private ... 0answers 900 views ### Public key Issue - same key pair as existing one? [duplicate] My question is a bit naive, but what if someone generates the same RSA key pair as someone else? This person would have the same private key and so would be able to decrypt messages not intended to ... 3answers 312 views ### Which area of Maths should I pursue? I would like to know which area of Mathematics would be most beneficial to cryptography. Surely Algebraic Number Theory and maybe to a lesser extend, Elliptic Curves, are closely linked to ... 5answers 53k views ### What is the lowest level of mathematics required in order to understand how encryption algorithms work? What mathematical fields of knowledge would be required in order to get a good understanding of encryption algorithms? Is it basic algebra, or is there a "higher education" mathematical field ... 2answers 690 views ### Major code breaks in history What are the major code breaks in the history of cryptography? Which code breaks changed the face of a battle or another major event? Which one had nationwide consequences? 1answer 4k views ### Examples of modern, widely used ciphers that suddenly fell? RC4 and GOST are two major ciphers (defined as being widely used to encrypt large amounts of data) that fell to cryptanalysis (relatively) suddenly. The first becoming totally broken and the second ... 0answers 1k views ### Strong encryption done by hand [duplicate] One of the distinguishing features of a good encryption algorithm, is that it is easy to encrypt, and hard to crack. Are there any that are easy enough for average folk to remember, and calculate by ... 0answers 198 views ### Simple but effective ciphers [duplicate] I enjoy cryptography, and like encrypting stuff hands on, for fun. I often send encrypted messages to friends. Trouble is, the easiest ciphers are also very insecure (for example, the Vigénère cipher ... 3answers 1k views ### Good challenges for a crypto competition for teenagers I'm holding a cryptography workshop for teenagers (around 16 years old) at our university. As part of the workshop, I'm planning to run a crypto competition with prizes: there will be different tasks, ... 1answer 470 views ### Single-purpose symmetric encryption scheme for single files I'm writing a simple password manager program that will encrypt/decrypt a single file (it's size will most likely stay under a few K). This is my initial file format design: ... 0answers 493 views ### Can you really trust WhatsApp's end-to-end encryption? [duplicate] I've seen many articles that actually trust WhatsApp's encryption and they may be right, but here is the thing that really makes me suspicious; all end-to-end encrypted apps I know, such as Telegram ... 1answer 276 views ### Structure for an introductory course on cryptography? Many introductory courses on cryptography have their treatment of secret-key crypto start with OTP, then block ciphers, and for public-key cryptography revolve around RSA with no notion of padding (... 1answer 2k views ### Need CryptDeriveKey AES implementation in C# I am integrating with 3rd party software that uses AES 128 encryption. I know this is not ideal, but the choice of encryption is up to the 3rd party software. I am using C#. My problem is in deriving ... 1answer 2k views ### What key exchange do OpenSSL and CryptoAPI prefer by default? Here is what I know. When I connect to a brand-new Linux Web server with Chrome and click the "lock" icon, the key exchange algorithm is described as "ECDHE_RSA". (Yes I know what that is.) When I ... 1answer 958 views ### Fast reduction in$GF(2^{128})\$ using x86 PCLMULQDQ

Modern x86 CPUs support the PCLMULQDQ instruction, which does an XOR-multiply of two 64-bit numbers instead of an add-multiply (i.e. typical arithmetic ...