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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AES256, repeated IVs and mostly-costant payload: how ok/bad is that?

I recently came across an application that more or less does this: starts from a (supposedly unknown to others) key generates a random IV encrypts some smallish (~ 160 bytes) payload with the key ...
3
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1answer
168 views

When to use HMAC alongside AES?

One of my clients wants to provide an URL to each of his customers to register in a system. This URL would contain a query string parameter with some data (e.g. code, email and name) from his clients ...
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1answer
216 views

How to secure my REST API once user authenticates with Google on mobile client?

In my application, I build REST APIs so that user can interact with my application server. Since I do not want to maintain User/Passwords, my iOS app authenticates client using Google. This all ...
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2answers
1k views

Reversible Hash Function?

Is there any reversible hash function? The hash function like SHA and MD5 are not reversible. I would like to know if there exist some reversible hash functions?
3
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1answer
69 views

What crypto prevents & detects “invisible” CAs? (e.g. in X509v4)

For this question, I'm calling an "invisible CA" one that Is signed by a root ca and exists as a 2nd or 3rd tier Is valid, not expired or revoked Has a different Public key than one that is ...
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1answer
138 views

Linux SSH and GPG

Can anyone please give me a quick crash course on SSH and GPG? SSH: What is the difference between public and private keys? Should I back up my ~/.ssh/ directory, what are the security implications ...
3
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1answer
130 views

How does OTR's authentication using “Question and answer” protect against MiTM?

I've read that the answer has something to do Socialist Millionaire, but I still don't understand how can the user be protected against malicious Man In The Middle, which would capture the question ...
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2answers
173 views

What are the alternatives to ECDSA for an authentication protocol?

In an authentication protocol, S has a public/private key pair known to C, and S and C have established a secure channel (for example, using DH or ECDH, or any other key exchange protocol). C wishes ...
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1answer
155 views

Publicly Available API + Sensitive ID/Key Transmission Over HTTP

I've run into a predicament... I'm developing a mobile application that utilizes a server for various things. One portion is that it stores an id/key pair related to accessing and processing ...
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4answers
385 views

Bastion host that allows jailed users to SSH but protects private key

Basically, I'm trying to let the user use a private key without having read access to it. Use case: Employee needs to SSH to a server in the data center. There is 1 private key for all servers, ...
2
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1answer
312 views

How does signing work with Elliptic Curve Crypto?

So I have read up and have a decent understanding of how the crypto works with Elliptic Curve Cryptography. I also think I have an understanding of how signing works with things like Elliptic Curve ...
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1answer
162 views

Advice on using encryption and hashing

I'm going to rephrase a question I asked earlier, as I don't think anyone understood what I meant. Bascially I'm writting a web based password locker, which can have multiple accounts; so that users ...
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1answer
87 views

Using encryption and hashing

I'm writing a project to securely store and share passwords between users, I've been doing tons of research into encryption algorithms, CSPRNGs, hashing algorithms, key stretching etc... I just want ...
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2answers
155 views

Securing a Shuffle Algorithm

After reading about writing a secure shuffle algorithm, I realized that my module that generates a password is only as strong as my PRNG, which in this case is Math.random(). I'm confused as to how to ...
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4answers
284 views

When do governments allow export of cryptography software?

I see this notice in the TextSecure README: The U.S. Government Department of Commerce, Bureau of Industry and Security (BIS), has classified this software as Export Commodity Control Number (ECCN) ...
5
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1answer
1k views

How are chosen plaintext attacks against ECB implemented in the real world?

Reading up on attacks against AES i have seen countless examples of why ECB is bad, and the logic behind it i can understand, but i can't get my head around how these attacks actually work in the real ...
2
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1answer
1k views

adding certificate that resides on smartcard to the microsoft store with private key ownership

how can we solve CryptAcquireCertificatePrivateKey fails with 0x8009200B when adding certificate from smartcard to local user store? in an enrollment system where users generate smartcard certificate ...
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2answers
103 views

Some questions about crypto

How to determine what type of encoding/encryption has been used? This link discusses in the first answer a "128 bit" value. How do you know that it is 128-bit and what is a 128bit value? If I md5sum ...
2
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1answer
109 views

What keeps the private key safe if an attacker has both clear and encrypted copies of a message and the public key?

Let's say someone obtained a message in both clear text and in its encrypted copy with asymmetric cryptography, like RSA-2048. He also has the public keys. Is the private key still undiscoverable? ...
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1answer
192 views

What are the enhancements of SHA1 compared to MD5?

I am looking for enhancements of SHA1 when its compared to MD5. But I am not talking about just heap sizes. I am talking about different enhancements than heap size. Also, I think md5 is faster than ...
2
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1answer
196 views

What cryptosystem makes the encrypted text look like random noise?

Suppose one wants to setup a cryptographic protocol in which 2 parties communicate using an encryption scheme that produces encrypted messages indistinguishable from random data (the desired property) ...
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2answers
207 views

Expiring AES Key

Is there any way to make an "expiring" AES key? Here's scenario to give a better picture: Say Bob has some data which he would like to share with Alice. Alice has a public and private key, let's say ...
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0answers
31 views

How digital certificate works? [duplicate]

I am trying to understand the digital certificate concept , but I am confused , Below goes my understanding & question, We are using Digital certificate because if Bob & Alice share their ...
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2answers
164 views

Is cryptography possible without volatile memory?

AFAIK, our current disk encryption methods (dm-crypt) preserve the key (as well as decrypted data) in RAM while the computer is running with an implicit assumption that the memory is volatile and key ...
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2answers
170 views

What is DVNC and how does it work?

As stated on their website: DVNC is not encryption but is a new branch of cryptography and information science. DVNC employs a new paradigm in secret keeping to keep your data secured. I ...
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2answers
184 views

If md5 is only insecure because of its speed, why doesn't this workaround make it reasonably secure?

I'm going to preface this by saying I have absolutely no clue when it comes to cryptography, but I'm posting this question because I'm very interested and I have no doubt there are some smart people ...
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4answers
1k views

How widely deployed is TLS with cipher ECDHE?

Microsoft deployed a patch for Windows 2012 R2 and Windows 8.1 that adds the following ciphers. Cipher suite Exchange Encryption Hash TLS_DHE_RSA_WITH_AES_256_GCM_SHA384 DH ...
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2answers
188 views

RSA-Based Signature Algorithms

From Beginning Cryptography with Java - chapter 4, digital signatures: Signatures are created using the RSA algorithm by applying the RSA algorithm using the private key and then distributing ...
6
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4answers
521 views

Why do you need a 4096-bit DSA Key when AES is only 256-bits?

This is something which I have been wondering and trying to find an answer for, but yet to come even remotely to one. Why do you need a 4096-bit DSA/El-Gamal key when AES uses only 256-bit keys?
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1answer
714 views

What's keeping a malicious man in the middle server from forging a valid certificate

According to process of authenticating a server certificate: What's keeping a malicious server to fill up a valid server certificate since it knows all the things: Forged Server public key (man ...
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1answer
144 views

Understanding cryptography practically [closed]

So I am interested in computer security, cryptography and security protocols. Thing is, everything I read is about theoretical usage of protocols, but how do those things work in real world? Is there ...
0
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1answer
80 views

Secure end-to-end when part of conversation must be over HTTP

We have a situation where a user's identity can be verified as follows: the network provider knows the identity of the user and injects secure headers into the HTTP request, which our servers can use ...
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3answers
779 views

Java AES encryption output length

I am trying to encrypt few database columns (string values) using Java AES algorithm. This is to protect certain sensitive data. For some users these data should decrypted. In Java AES encryption, if ...
3
votes
2answers
557 views

Is AES(Rijndael) faster than Blowfish?

I know theoretical that blowfish is much faster than aes. But I benchmarked several algorithms including aes and blowfish for 1MB, 5MB, 10MB etc. files in java 8 platform and bouncy castle library. In ...
3
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1answer
652 views

Open source solution to capture and decrypt SSH traffic (with private key)?

I am looking for a free open source solution that is able to capture and decrypt SSH traffic given the fact that I can provide the server's RSA private key (something like SSH CryptoAuditor). Please ...
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1answer
776 views

How do we estimate the time taken to crack a hash using brute force techniques

A German hacker famously managed to brute force crack a 160 bit SHA1 hash with passwords between 1 to 6 digits in 49 minutes. Now keeping everything constant (hardware, cracking technique - here ...
2
votes
1answer
185 views

Stream/Block encryption using XOR and Hash function?

Could a hash function like sha1 or ripemd-160 be used for secure key generation in a stream/block cipher? Obviously a repeated key like "abc123abc123abc123" would be bad, and a one time key pad would ...
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1answer
1k views

Safety of TrueCrypt hidden volumes

According to the documentation a hidden volume stays hidden because it appears as free space. In TrueCrypt free space always has random data in it, however in the case of a hidden volume it's not ...
2
votes
1answer
330 views

How secure is Vigenere cipher for random data?

Traditional situation It is easy to crack a ciphertext encrypted by Vigenere cipher, if you know the plaintext is in a natural language like English. There are two methods to discover the key used to ...
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1answer
200 views

Knowing Input&Output, How to determine encode method and the passkey that was used in encoding?

I've looked on this site and on SE. but I couldn't get a handle on this. Is there a way to find what type of encoding (and/or encode key) is being used? For example, I am testing a web ...
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1answer
226 views

Should I keep all UUIDv4 generated oAuth2 Bearer Tokens in my database to prevent an attack?

I generate oauth2 access and refresh tokens and store them in my database. I generate these tokens using UUID v4 and remove the dashes. I used to delete the tokens after they expire but now I store ...
0
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1answer
89 views

Public Key Authentication

Is there another way to verify someones public key without a CA signing it? A challenge-response authentication including some sort of UID of the smartphone? Smartphone A generates asymmetric key ...
3
votes
5answers
359 views

How does one know when a message is successfully decrypted? [duplicate]

How do people who decrypt encrypted messages know they have decrypted to the correct message? Do they just keep decrypting until the message is in English (or any other language), or is there a ...
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2answers
82 views

Symmetry meaning in cryptographic algorithms

When we refer to symmetry in cryptographic algorithms such as symmetric or assymetric does the symmetry refers only to the equality or not of the keys, or does it also refer to the symmetry of ...
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2answers
209 views

Asymmetric vs Symmetric Encryption Benchmarks

I have found these benchmarks in Crypto++'s site. http://www.cryptopp.com/benchmarks.html But I am, quite honestly, not entirely sure how to interpret them. I am really looking for a set of ...
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3answers
1k views

Why is RSA decryption slow?

I've been researching the disadvantages of using RSA for encryption, and one I've found repeatedly is that RSA decryption is slow, but I haven't seen an explanation as to why this is. Can anyone ...
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5answers
2k views

Whenever an unhandled exception somehow makes it into production, is it safe, viable, etc. to print an encrypted stack trace to the end user?

Whenever an unhandled exception makes it into production somehow - whatever the reason - there's generally an option (especially with .NET programs) to print out a stack trace to the end user before ...
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1answer
56 views

Is it safe to use the Keccak Algorithm to create the Key for a Serpent cipher?

I like to store some configuration but would encrypt them with the Serpent cipher. Is it safe to do this? When not, what is a better solution?
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1answer
278 views

Can I use crypto.getRandomValues to create a private key?

In the window.crypto spec: http://www.w3.org/TR/WebCryptoAPI/#RandomSource-interface It says explicitly: "Do not generate keys using the getRandomValues method. Use the generateKey method ...
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1answer
198 views

How to fix this broken crypto protocol?

I am considering a protocol where you upload a one time pad to a server, using public key encryption and then the result (using the pad) is sent back in plaintext: Alice uses Bobs RSA public key to ...