Cryptography is the practice and study of logical means used to achieve information confidentiality, integrity and authenticity. It covers, among other things, encryption (making some data unreadable except for those who know a given secret element, called a key), data hashing (in particular for ...

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955 views

Public key length

I was wondering if there was (and I hope there is) a standard for public key size for ECDH (Elliptic Curve Diffie-Hellman) and ECDSA (Elliptic Curve Digital Signature Algorithm) for every curve type ...
4
votes
2answers
6k views

Can DES-based hashed password be recovered if salt is known?

Can a hashed password be recovered if the hashing is done with DES based crypt function in PHP and both the hash and salt are known by the attacker? Consider the following example: $salt = 'mysalt'; ...
14
votes
2answers
981 views

Salting password with the first 8 bit of the password itself

Do you guys think salting password with the first 8 bit of the password itself will have same result as using stored salt to hash password? [Clarification] I am not storing salt but creating from the ...
6
votes
3answers
995 views

chosen plaintext attacks against MD5 and SHA1

According to http://tools.ietf.org/html/rfc2617#section-4.9, having the server chose a nonce but not having the client chose a nonce opens up Digest Access authentication to chosen plaintext attacks. ...
2
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2answers
207 views

Which private-key encryption should I use for server to server communication?

I am tempted to write my own which covers: Checksum to ensure data is not tampered with. Long and multiple rotating keys so that it is (practically) impossible to decrypt. Will use /dev/random for ...
12
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2answers
990 views

Is there any advantage of bcrypt over multiple iterations of SHA-x/MD5?

I know that a good password hashing algorithm should be slow. MD5, SHA256, etc. are fast. So I've been adding multiple iterations of SHA-256 hashing to my web apps (around 50000). Getting the hash of ...
140
votes
3answers
113k views

What's the difference between SSL, TLS, and HTTPS?

I get confused with the terms in this area. What is SSL, TLS, and HTTPS? What are the differences between them?
1
vote
1answer
638 views

Nonce construction for CTR mode (Mcrypt)

Edit: I'll put up this more clearly. By the most simplest form, I'm asking that if I AES encrypt in CTR more with Mcrypt (using PHP), can I create the "IV" by just simply reading 16 bytes from ...
13
votes
3answers
1k views

What's the mathematical model behind the security claims of symmetric ciphers and digest algorithms?

Why can SHA-1 be considered a secure hash function? That's something I still wonder about. I understand the concepts of why modern asymmetric algorithms are deemed to be secure. They are founded on ...
230
votes
7answers
176k views

RSA vs. DSA for SSH authentication keys

When generating SSH authentication keys on a Unix/Linux system with ssh-keygen, you're given the choice of creating a RSA or DSA key pair (using -t type). What is the difference between RSA and DSA ...
1
vote
2answers
201 views

TCrypto - Comments about design decisions I made?

I have pushed some code to GitHub to demonstrate the usage of symmetric key encryption in PHP. It is a small key-value storage library and it (optionally) offers ability to encrypt the stored ...
4
votes
2answers
1k views

When should I use Message layer encryption vs transport layer encryption

Basically I will be having to secure a connection between different hops. Therefore even if TLS is widely known to be the best in class, I am wondering that in such a case message based encryption ...
0
votes
1answer
172 views

Safer k128 key schedule

Can someone explain to me how safer 128's key schedule works? there are many parts that make no sense because they were not described at all in the paper (pages 3 and 5 in the pdf). The second ...
4
votes
1answer
421 views

Asynchonous Linear Feedback Shift Register : test vectors

Well I've been working on coding LFSR structures for my research projects. Being able to find sources on the subject, I've been able to test a single LFSR with different initialisation and TAP ...
5
votes
1answer
950 views

Is the DES “mangler” function invertible?

The DES symmetric cipher is based on a Feistel network operating repeated on 32-bit halves of the 64-bit block. The usage of Feistel means that the "mangler" function used does not need to be ...
14
votes
1answer
7k views

Does Windows really still use unsalted MD4 for password storage?

I find it quite difficult to believe that the passwords in Active Directory for Windows 2008 R2 are still stored using the unsalted MD4 (aka "NT Hash") algorithm. Can it really be true? I've been ...
3
votes
1answer
265 views

Pseudo-Hadamard Transform in SAFER K-64

The PHT seems so simple: b1 = 2*a1 + a2; b2 = a1 + a2. and yet, i am definitely missing something, since the paper for SAFER K-64 shows: INPUT VECTOR is 0 0 0 0 0 0 0 1 OUTPUT VECTOR is 1 1 1 1 1 1 ...
15
votes
3answers
525 views

What is gained by hashing the last block on-device?

Recently I encountered the notion of "hashing the last block on-device". It means that when computing a digital signature, the hash that serves as input for the actual signature computation is not to ...
7
votes
3answers
3k views

DUKPT - how does the receiver verify the transaction counter?

I have one question regarding this document: ANSI X9.24, Retail Financial Services Symmetric Key Management Part 1: Using Symmetric Techniques In the chapter "Method: DUKPT (Derived Unique Key Per ...
12
votes
6answers
2k views

Identity-Based Encryption - how secure is it?

I was always taught never to invent my own crypto algorithm, and never to trust someone who has a proprietary algorithm. I'm looking at Voltage SecureMail, which uses IBE (identity-based encryption) ...
8
votes
3answers
724 views

zero knowledge proof and its protocol

In Zero-Knowledge Proof where we take the analogy of Peggy (Prover) and Victor (Verifier): In this story, Peggy has uncovered the secret word used to open a magic door in a cave. The cave is ...
2
votes
2answers
499 views

GOST cipher test vectors

Does anyone know where to find test vectors for the GOST cipher? I have been looking around for quite some time, and have been unable to find anything. I know that the sboxes are dependent on the ...
5
votes
4answers
1k views

Using password hash as session ID?

For a rich client web app, on the server I need to verify that each call comes from a legally logged in user. Obviously user ID is not enough, because that's easy to guess. I have an idea I am ...
19
votes
4answers
2k views

What to transfer? Password or its hash?

Let's say in my database I store passwords hashed with salt with a fairly expensive hash (scrypt, 1000 rounds of SHA2, whatever). Upon login, what should I transfer over the network and why? Password ...
11
votes
4answers
2k views

Using computer random number generators to produce keys, it is secure?

Does generating an encryption key using the random number generator on one's computer present a security risk? If so how might that risk be mitigated, specifically when generating RSA key pairs in ...
12
votes
5answers
4k views

Use RSA keypair for PGP encryption and decryption

Is there a way that I can use a RSA keypair with PGP? What I mean is that I have 2048 length keypair and i want to use that to encrypt and decrypt data. But all I have found is that the PGP uses some ...
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votes
3answers
418 views

Would this kind of encryption be good at anything?

I have put much thought into this very simple algorithm and I have no clue if it was thought before... But I think it should have. I also know nothing about other encryption algorithms so I can't tell ...
4
votes
2answers
3k views

mysql AES_ENCRYPT key length

AES_ENCRYPT uses a 128 bit long key to encrypt the data, but how does mysql handle longer or shorter keys? I found out that pycrypto for instances recomend to transform the key by using md5 sha1 sha2, ...
41
votes
5answers
5k views

How do some sites (e.g. online banks) only ask for specific characters from a password without storing it as plaintext?

I thought How can a system enforce a minimum number of changed characters... would answer my question, but it seems this is a different case. When I sign on to my online banking account, I'm prompted ...
25
votes
6answers
23k views

Most secure password hash algorithm(s)?

What is/are currently the most cryptographically secure hashing algorithm(s)? (available in PHP) Speed is irrelevant, because I'm iterating the hash over a fixed time (rather than a fixed number of ...
8
votes
4answers
4k views

moving from MD5 to SHA-512

This question is more of a security policy than a technical security question. Many years ago I developed an asp.net site, implemented Forms Authentication, and stored the user passwords as MD5 ...
7
votes
1answer
271 views

Collision attacks on OCB?

I've been looking into the OCB cipher mode and everything I hear sounds good. I was planning on implementing it. Everything except for this lone voice, that is: Collision attacks on OCB: We ...
4
votes
3answers
4k views

Vigenere Cipher - help with decryption (by hand)

So this is a Vigenere cipher-text EORLL TQFDI HOEZF CHBQN IFGGQ MBVXM SIMGK NCCSV WSXYD VTLQS BVBMJ YRTXO JCNXH THWOD FTDCC RMHEH SNXVY FLSXT ICNXM GUMET HMTUR PENSU TZHMV LODGN MINKA DTLOG HEVNI ...
4
votes
3answers
233 views

Choosing an authenticated encryption cipher mode without associated data

In the application I'm writing there is need for a huge amount of private data transfer on the order of eighty gigabytes, but there is no public data. I'm looking especially to gain ...
6
votes
1answer
2k views

What is the purpose of AEAD?

I think I need to correct some misunderstandings I have about AEAD. What is associated data used for in authenticated encryption?
5
votes
2answers
232 views

OMAC: multiplication in a finite field - how can I compute the correct polynomial

From The EAX Mode of Operation: We explain the notation used in the definition of OMAC. The value of iL (line 40: i an integer in {2, 4} and L ∈ {0, 1}n) is the n-bit string that is obtained by ...
3
votes
1answer
129 views

What is the benefit to using a two-pass AE scheme rather than one-pass?

What benefit is gained using a two-pass AE or AEAD scheme rather than a one-pass? Two-pass is roughly half the speed.
34
votes
4answers
20k views

Are salted SHA-256/512 hashes still safe if the hashes and their salts are exposed?

Scenario: a database of hashed and and salted passwords, including salts for each password, is stolen by a malicious user. Passwords are 6-10 chars long and chosen by non-technical users. Can this ...
4
votes
2answers
146 views

A method for securely sharing centrally-stored documents among a changing set of users?

I believe it's possible to meet these requirements only if a third party is involved in a manual process. For example: Each user is given the same public key The private key resides offline at a ...
8
votes
3answers
606 views

Which authentication at the end of the Secure Remote Password protocol?

For the the client and server to prove to each other that they have the same premaster shared key, the original author suggests this: M = H(A | B | K) --> <-- H(A | M | K) ...
6
votes
1answer
3k views

Is this how to implement CTR around a system that only implements CBC, CFB, CTS, ECB and OFB?

The encryption library in my programming language does not support CTR, though it supports CBC, CFB, CTS, ECB and OFB. I'm assuming it is theoretically possible to securely implement CTR around one ...
9
votes
1answer
371 views

Optimal variable sizes in the Secure Remote Password protocol

I am implementing the Secure Remote Password protocol: U = <username> --> <-- s = <salt from passwd file> a = random() A = g^a ...
12
votes
3answers
2k views

When using AES and CBC, can the IV be a hash of the plaintext?

[Originally on programmers.stackexchange.com with title: Can you encrypt with AES+CBC and search the encrypted data] Basically, I'm going to go with Advanced Encryption Standard with either ...
5
votes
2answers
4k views

Tool or Process to check for AES-NI support on processor?

In another question, Thomas' answer mentioned the AES-NI instruction set, which piqued my curiosity. Is there a tool or process available out there to check whether the instruction set is available ...
8
votes
1answer
1k views

How to choose a stream cipher

Are there high-speed ciphers designed for things like internet streams without sacrificing security? There are so many options that operate in stream mode. How would one choose a cipher?
6
votes
2answers
643 views

Implementing Secure Remote Password: Constructing the verifier

The SRP protocol as described in RFC 2945 generates the password verifier: x = SHA(<salt> | SHA(<username> | ":" | <raw password>))` v = g^x % N I have three questions: why use ...
17
votes
2answers
4k views

Why is it always `HASH( salt + password )` that we recommend?

Browsing over this site, many forums, online articles, there's always one specific way we're suggesting to store a password hash: function (salt, pass) { return ( StrongHash(salt + pass) ) } But ...
3
votes
1answer
94 views

Differing scrambling parameter generation methods in Secure Remote Protocol

RFC 2945 (The SRP Authentication and Key Exchange System) states, The parameter u is a 32-bit unsigned integer which takes its value from the first 32 bits of the SHA1 hash of B, MSB first. ...
6
votes
3answers
1k views

Using Secure Remote Password without sending the username in the clear

To initiate a key exchange using the SRP protocol the client sends the username so the server can look up the salt and password verifier. Is there a simple way to change this so that an evesdropper ...
5
votes
1answer
268 views

Using Secure Remote Password without embedding the modulus

The SRP protocol as described by the author assumes that the large safe prime modulus and generator are embedded into the client and server rather than being transmitted as part of the protocol. ...