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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How much security is compromised if we accept other characters as login (other than the original password)?

I've just realised that facebook accepts 3 forms of a password: Source: Facebook actually accepts three forms of your password: Your original password. Your original password with the ...
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What are the differences between the versions of TLS?

Please correct me if I'm wrong, but my understanding is that SSLv3 and TLSv1 is just a rename of the earlier protocol... but TLSv1 adds the ability to have secured and unsecured traffic on the same ...
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Generate cryptographically strong pseudorandom numbers in Javascript?

Is there any good way to generate cryptographically strong pseudorandom (or true random) numbers in Javascript? The crucial requirement: if a.com's Javascript generates some random numbers, no one ...
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What was SSL 1.0?

What was SSL 1.0? SSL 2.0 and 3.0 are well-known and well-documented. But what did the SSL 1.0 protocol look like? Wikipedia says there was a SSL 1.0 but doesn't say anything about how it worked. ...
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Is there a length beyond which increasing password length provides no additional security?

Assuming that the password is stored hashed and salted, and that it is a string of random characters, is there a point where adding to password length doesn't add security? Since the hash will have a ...
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769 views

In the recent DKIM vulnerability, how did someone determine key length by looking at headers?

Having read this recent article : Wired-DKIM vulnerability, I have a couple of questions. How can one determine the key length that is being used simply by looking at the headers ? And I'm assuming ...
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Is there an organization that reviews/approves crypto implementations?

As I understand it, NIST approves crypto algorithms but doesn't cover specific implementations. I think I've read about IEEE approving hardware implementations of, e.g. AES, but I can't think of any ...
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Describe an example of indistinguishability obfuscation or functional encryption

As described in Perfecting the Art of Sensible Nonsense, a major breakthrough in cryptography research was published in the summer of 2013: Candidate Indistinguishability Obfuscation and Functional ...
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Location to store an encryption key

I'm building a secure system which stores messages on a server in a Postgresql database. The messages are stored encrypted with PHP's openssl_encrypt() function with the AES-256-CBC method. At the ...
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HMAC Based Request Signing - Storing the Salt

I'm working on a (non high security) project that currently isn't live but might go live at some point. We have a REST API (implemented using Restlet and Neo4j) running on a server and an Android ...
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1answer
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Where do I get prime numbers for Diffie-Hellman? Can I use them twice?

I realise it's very hard to generate suitable prime numbers and generators for the Diffie-Hellman key exchange. What is the best way to generate them? And if I have one, can I use it twice? ...
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What are the practical uses of large asymmetric keys?

The Windows CNG supports keys of varying sizes, e.g. RSA up to 16384 bits: http://msdn.microsoft.com/en-us/library/windows/desktop/bb204778(v=vs.85).aspx. My understanding is that in crypto today we ...
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600 views

Is it preferable to perform encryption using database functions or code?

Several databases I am familiar with provide functions or modules for encryption. Examples include dbms_crypto for oracle databases and built-in functions for MySQL. Most of the commonly used ...
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420 views

How do new security and cryptography techniques/protocols avoid the chicken-and-egg problem?

. . .better solutions have been proposed and will be worth considering once they have withstood the test of time (i.e. “5 to 10 years in the field, and not broken yet”). -From Thomas Pornin's ...
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If I am obliged to store a password/certificate on a client side, how can i make sure that it is protected?

In certain cases we need to establish a key/password/certificate as a first timer and then as a client we need to use this key/password/certificate to get authenticated. Therefore the ...
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Is Changing a File Type and Name an Effective Security Solution?

Is renaming folders & files and changing file types an effective solution for file security of a PC? I am an application programmer and have an extensive background in it. I have written a ...
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6answers
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Security of SHA256 and Bitcoins

The Bitcoin network use SHA256 as a core component to it's design. I'm no expert on cryptography, but it seems to me it usually is only a matter of time before security vulnerabilities are discovered ...
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3answers
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What is the DUKPT Key Derivation Function?

I'm tasked with decrypting ciphertext acquired from an encrypted card reader. The card reader utilizes DUKPT(derived unique key per transaction) scheme and 3DES encryption. I don't have a problem with ...
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5answers
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What does “key with length of x bits” mean?

I'd like to know what it means to say "the cryptosystem C uses keys with a length of x bits". I do not understand what the bits length means... doesn't it depend on the encoding? The same word encodes ...
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Is Schneier's “Applied Cryptography” current?

I've been recommended Bruce Schneier's 1994 book Applied Cryptography as an introduction to the use and the inner workings of cryptography. Is this book still current and a good introduction?
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Encryption decryption time

Does the encryption / decryption time of rsa algorithm vary significantly with a change in key length? For example, is there a noticeable difference in encryption/decryption time between 512 bit and ...
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2answers
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Is 1024bit Diffie Hellman key exchange secure?

My system uses AES-256, 4096bit RSA CA key and 2048bit RSA keys for servers together with SHA-256 signing. Does using 1024bit DH key exchange lower its security? I read on one mailing list that ...
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How does a weakness in a random number generator lead to a compromise of the entire cryptographic process?

In the news, there are several articles (here, here, and the technical point of view) which have to do with a weakness in a random number generator. The question is somewhat twofold. What symptoms do ...
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How can I mitigate the threat that DPAPick poses to my DPAPI protected data?

The Windows Data Protection API (DPAPI) is the suggested method for storing secrets on Windows systems (such as database passwords required by ASP.Net applications). DPAPick was presented at BlackHat ...
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SSL Certificate revocation check

In the SSL protocol I don't see where the certificate is checked for revocation status. https://developer.mozilla.org/en/Introduction_to_SSL Is the Certificate Revocation and Status Checking not ...
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Recommendations for a Certificate Management tool for Linux [closed]

A client is looking to roll out OpenVPN to all its mobile employees and will use certificates on both the server and all clients. This creates a new challenge to manage all these certificates and ...
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How does the padding scheme impact the security of encryption

After digging a little deeper into cryptography I am wondering what impact the different padding schemes do have an the security of an encryption algorithm. Lets take AES-128 in CBC mode as an ...
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4answers
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Tool for public key cryptography where password is the private key?

Is there any free & open source tool for public key cryptography, where the private key is just a chosen password? Here is what I need: I want to make backups every hour using a script I want ...
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3answers
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Is TDEA (TripleDES) invulnerable to the weak keys of DES?

The key space of DES includes some keys that are weak, which results in a ciphertext that is extra vulnerable to cryptanalysis. Is TDEA (also known as TripleDES) invulnerable to those weak keys? Or, ...
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Suitable cipher for SMS encryption

I would like to create application for encrypting SMS messages. After long enough discussions I decided to use symmetric encryption, since handling public/private keys issue is too difficult for most ...
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715 views

When brute-forcing DES, does knowing something about the plaintext help?

Data Encryption Standard (Wikipedia) I know that with brute force there are 2^56 possible keys to check (56 bits, each either a 1 or 0). But let's say I know the message itself is only made up of ...
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1answer
206 views

Securing a prediction about a future event

I want to make a prediction about a future event, but only reveal that prediction after the event occurs lest knowledge of my prediction affect the outcome. For example, suppose Alice predicts that ...
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882 views

AES using derived keys / IVs. Does it introduce a weakness?

I'm looking for an efficient way to encrypt multiple fields in a database with AES using a single global key, used throughout a large web application. Obviously in order to re-use this key, a unique ...
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1answer
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SSL replay attack when client/server random is missing

Hey studying the SSL protocol, I'm wondering how can someone be able to do a replay attack if the server nonce is missing? All the material I find says that nonces prevent it, but theres no examples ...
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1answer
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TLS replay attack - requirements of the serverHello nonce

As you all know, the SSL/TLS protocol requires both client and server to exchange (in clear text) a random number or nonce. This is presumably used to prevent replay attacks. It is not clear to me ...
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2answers
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Why do PGP master keys only have a single subkey, and tie certification with signing by default?

After learning more about PGP subkeys and how to split apart the roles of (S)igning, (E)ncryption, (A)uthentication and (C)ertification, I discovered that in most cases(?) a default master key has a ...
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3answers
471 views

Are there any smartcard/hardware-tokens for certificate-based authentication which are easily destroyed?

It's all very well to use multi-factor authentication, but supposing you want to 'destroy a factor' so that in an situation where you are likely to be coerced to provide your passphrase, you can ...
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2answers
2k views

Data Encryption and Key Management in C#

Which route to take, what are the pros and cons, which is more secure.. Generate AES key, encrypt the data with it and then encrypt the AES key with RSA, save the encrypted data and encrypted AES ...
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2answers
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Estimating the size of a rainbow table

What are rainbow tables and how are they used? Gives a very precise answer about what rainbow tables are and how they are used. I had always confused hash-tables and rainbow tables. My question is ...
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1answer
360 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 ...
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3answers
1k views

Does the entire AES encrypted dataset have to be present to be 'cracked'?

I am implementing an AES 256 algorithm on credit cards and I am wondering if I would be strengthening or weakening the encrypted dataset if I split the dataset and persisted it in two locations. I ...
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4answers
368 views

Atypical DRM situation: distribute pictures to select partners, then prevent them from reusing them

We want to distribute digital content (think pictures) to a select number of partners (around 1000, worldwide) to use as visual reference. We would like however to prevent them from copying or in any ...
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7answers
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Is there any asymmetrically encrypted file system?

Is there a file system providing a directory where everybody can write, but only the directory owner can read the files? In theory it could be done by encrypting using the public key while writing, ...
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3answers
2k views

Certificate authorities for a PKI

Some people think the certificate authorities for a PKI should be the government, but others think certificate authorities should be private entities, such as banks, corporations, or schools. What are ...
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397 views

What can one do when encryption methods fail?

I'm in search of an expert to answer my curiosity. Suppose that methods like AES/DES, SSH, PGP, RSA, etc. can be cracked or fail somehow. In other words, suppose that it's possible to determine one ...
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3answers
3k views

What common products use Public-key cryptography?

I want know what common use products are there that use public key/private key cryptography?
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time to crack file-encryption password - more than just iteration

I have often seen that takes x amount of time to crack a certain length password. But this just seems to be the amount of time it takes to iterate through all the possibilities. What about the time it ...
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Is using HMAC to transmit a password OK?

I'm writing a small webapp and I don't want to transmit login passwords as cleartext. As I don't have SSL available I've written a one-time challenge system which sends a random string with the login ...
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4answers
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What Partial Homomorphic Encryption implementations exist and how do I leverage them?

It appears that only Partial Homomorphic Encryption(P.H.E.) is practical for modern day (2011) use. However I'm having difficulty locating libraries (FOSS or otherwise) that enable me to leverage ...
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Can the numbers on RSA SecurID tokens be predicted?

My workplace uses these SecurID tokens which provide you with a temporary password, the code will expire after a short time. I have always been fascinated by the things, because it seems as though ...