e-sushi
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Can I compute “SHA256(secret||data)” when having “SHA256(secret)” and “data”?
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As @yyyyyy already commented: if you are able to successfully apply a length extension attack, you would be able to compute $$\operatorname{SHA256}(\mathit{secret}\Vert\mathit{padding}\Vert\mathit{...

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How to brute force sqlcipher encrypted file with MD5 hash of a 7 bit key?
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As SEJPM already hinted at in his comment, a 7 bit key is short enough to allow a plain and simple brute-force attack because there are merely 128 different keys to be tested. Hint: 7 bit = 1111111 = ...

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Difference between actual attacks and theoretical attacks on SHA cryptographic series
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A theoretical attack is an attack strategy that was born out of “theory”, “calculation”, and — in the least cases — “simulation”. Yet, the strategy is yet to be proven in practice. An actual attack ...

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Is $G$ a secure PRG?
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To give this question its deserved answer, I’ll repeat what Ricky Demer noted in his comment: $$G(x \oplus 1^s) = F(k,x \oplus 1^s) \oplus F(k,x \oplus 1^s \oplus 1^s) \\ \downarrow \\ F(k,x \oplus ...

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Does this chat protocol exist?
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For this they have to register their public keys in a server: Alice generates her public and private keys (pub_A, priv_A). Alice sends pub_A to a public server. Bob generates his public ...

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Crypto hash function vs encryption algorithms
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The speed of individual algorithms strongly depends on their implementation. This goes for both hashing algorithms as well as encryption algorithms. This quickly becomes clear if you take a look at ...

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In cryptographic protocols, what protects against an attacker dropping messages?
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Assuming that your question excludes any kind of “regular” transmission error (which might also lead to one of the messages not reaching the receiver) the receiver should regard message #236 to be ...

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SHA512withRSA - Looking for details about the Signature Algorithm
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References Related to your reference request: SHA512withRSA points to the RSA Signature Scheme with Appendix based on PKCS #1 v1.5 with SHA-512 hash function. This means you’re looking for reference ...

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Encrypt HDD with keyfile and password and allow backing up the keyfile with secret sharing
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Is /dev/urandom fine for my use-case or should I use /dev/random? Theoretically, there is no security difference as both are regarded to be cryptographically secure RNGs. Practically, you’ll want ...

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Question about dual system encryption
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In these systems, is adversary able to generate semi-functional ciphertexts? Quoting the paper figlesquidge mentioned in a comment: Crypto 2009 Dual System Encryption: Realizing Fully Secure IBE ...

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DH key exchange with only one end authenticated
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…what if I only verify the signature of one end? Bob would not be able to know if he is looking at a signature by Eve, or if it’s a valid signature coming from Alice. In case if Eve is messing with ...

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Uncompress password protected WinRar file without password
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According to the RarLab website as well as the RAR changelogs, the encryption algorithm of (Win)Rar was changed to AES (Advanced Encryption Standard) with a 128 bit key length, starting with version 3....

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What is the difference between authenticating and signing a document?
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To keep it simple: authentication = something to indicate the origin and authenticity of a document or message. signature = a form of identification in authorizing a document or message. You can ...

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Is symmetric encryption no longer necessary?
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Symmetric encryption is no longer necessary, because all security services can be implemented with public-key cryptography. That's a strong claim which, in it's current state, lacks references and - ...

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Is the following authentication protocol insecure?
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For one-way authentication (where Bob is the server and Alice the client), I would rather do something like this: Alice → Open Connection → Bob Alice ← $R$ ← Bob Alice → $K_{A-B} (R)$ → Bob By ...

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Authentication of machine before installation (to stop piracy)
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Thinking "crypto"… One way I could imagine how you achieving at least some kind of copy-protection on your PHP-based scripts is to use solutions like these random search results: sourcecop, ...

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Is there a name for this 'enhanced' caeser shift and if so, is it trivial to break?
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Identification There isn't a specific name that describes this as an individual cipher. It is indeed a "Caesar cipher" that merely differs from the cipher Julius Caesar himself used as it ...

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Calculating ciphersize of Paillier, SSE and OPE
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In Paillier, the size of ciphertext is about the double of the plaintext. (Might be interesting for you to read: http://courses.engr.illinois.edu/cs598man/fa2011/slides/ac-f11-lect15.pdf‎) For Order-...

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How should I interpret this note on diffusion of the internal state of a PRNG?
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According to the text you quoted — yes, it's less quality and you should (following math logic) loop the $\textit{MIX-i}$ at least (26/8=) 3 times to achieve the same amount of flipped bits as the "...

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Different patterns of different paterns, wildcard
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Generally, that is possible. crypto-analytics Including solutions that collect statistical information, there are several solutions which are used during cryptographic analytics that can cope with ...

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RSA padding: what is it and how does that work?
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Padding in cryptography means adding a (mostly secret) random set of data to the cryptographic functionality. In practice and when done correctly, cryptographic padding adds a cryptographic problem ...

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Selective format-compliant JPEG encryption?
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Selective format-compliant JPEG encryption as you are trying to do it is a great idea, but it won't work... not like this. To keep the reasons short and simple: JPEG uses lossy compression (and ...

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Size of A Hashed String Using SHA-512
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When hashing a messages of size of n, does the SHA2 algorithm always produce the same sized hashed value? SHA-2 output is always fixed. SHA-512 will always produce a message digest of 512 bits – ...

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secretKey ⊕ (secretKey ≪ 1), is randomness lost?
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Converting my comments into an answer: If your secret key is cryptographically secure, you don't really gain anything by applying such a shift-XOR — but indeed, there is no entropy loss. What's a ...

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Is container format relevant to security of encrypted message inside?
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Converting the comments to an answer… Ricky Demer: "algorithms used" should be stored with the key(s). "compression of plaintext used, probably a user supplied tag" should go into the MAC. ...

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Definition of randomly generate in the parallelepiped
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As @LeoDucas already commented, the answer is contained in Appendix E (page 22) of the same paper:

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Modulo properties of two prime numbers
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Recall the definition for when two numbers are congruent modulo some number. Now, prove to yourself that if two numbers are congruent modulo some product, they are also congruent modulo the factors ...

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