# Tagged Questions

Cryptanalysis is the part of cryptology dedicated to the mathematical analysis of the weaknesses of cryptographic algorithms, the goal being to defeat some of the security properties that the algorithm should fulfill, e.g. decrypting data which has been symmetrically encrypted with substantially ...

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### How to determine what type of encoding/encryption has been used?

Is there a way to find what type of encryption/encoding is being used? For example, I am testing a web application which stores the password in the database in an encrypted format (WeJcFMQ/8+8QJ/w0hHh+...
16k views

### How would one crack a weak but unknown encryption protocol?

I was reading this interesting question: Is my developer's home-brew password security right or wrong, and why? It shows a weak home-brew algorithm developed by "Dave", and the answers discuss ...
13k views

### What kinds of encryption are _not_ breakable via Quantum Computers?

There's the recent article NSA seeks to build quantum computer that could crack most types of encryption. Now I'm not surprised by the NSA trying anything1, but what slightly baffles me is the word "...
68k views

### How to estimate the time needed to crack RSA encryption?

How to estimate the time needed to crack RSA encryption? I mean the time needed to crack Rsa encryption with key length of 1024, 2048, 3072, 4096, 5120, 6144, 5120, 7168, 8192, 9216, 10240, 11264, ...
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### Should RSA public exponent be only in {3, 5, 17, 257 or 65537} due to security considerations?

In my project I'm using the value of public exponent of 4451h. I thought it's safe and ok until I started to use one commercial RSA encryption library. If I use this exponent with this library, it ...
22k views

### Where can I learn cryptography/cryptanalysis the hard way, without going to school ? Any good book?

I'm not so bad at mathematics: I know what are p-list and p-combinations, I know matrix algebra, I know what a XOR is, I know how to tell if number is a prime, etc: I'm not the programmer who hates ...
3k views

### If someone breaks encryption, how do they know they're successful?

Let's say I have a file containing a random bunch of bits and then I encrypt it using some modern algorithm (Blowfish, AES, or whatever). If someone captures the file and mounts a brute force attack ...
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### Why haven't (most of) the Zodiac Killer's letters been decrypted? [closed]

The Zodiac Killer (who, in fact, is not Ted Cruz) was a serial killer in the late 60's and early 70's. The twist is, he would frequently taunt the local press with cryptic letters. Four of these ...
7k views

### Cracking a linear congruential generator

I was recently listening to the security now podcast, and they mentioned in passing that the linear congrunential generator (LCG) is trivial to crack. I use the LCG in a first year stats computing ...
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### WPA significantly less secure than WPA2?

I understand at least theoretically WPA2 is more secure than WPA, but in practice does it make any difference which one you use? From what I know there are no known attacks for either except for ...
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The password hash used for MySQL passwords prior to version 4.1 (now called OLD_PASSWORD()) seems like a very simple ad-hoc hash, without salts or iteration counts. See e.g an implementation in ...
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### 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 ...
3k views

### At what point does adding more iterations to PBKDF2 provide no extra security?

If my true passphrase is used only to generate a hash which is used as the cipher's actual key, doesn't that mean it's possible to try and brute force the cipher itself? I know it would take an ...
669 views

### Is a large number of RSA-encrypted files a vulnerability?

Would having a large number (10^4) of RSA encrypted files make it easier for an attacker to find my private RSA key? Update: These files would be available to the attacker, and perhaps the content of ...
1k views

### Correct way to get a number from 0-9 from a random byte?

If I have a good random number generator that gives me a byte of data at a time, and I want to extract a random decimal digit of 0 to 9 from that byte stream, what is the correct way to do that? At ...
4k views

### 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 ...
3k views

### Length of CSRF Token

Is there any standard length of the token which should be used while generating the random tokens? Should we use the same standard which we use for generating Session IDs?
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### 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 ...
1k views

### Does repeating one word to form a password result in a similar pattern in its encrypted format?

If i use a single word to form a password by repeating it like the examples below: securesecuresecuresecuresecuresecure SeCuReSeCuReSeCuReSeCuReSeCuReSeCuReSeCuRe \$eCuRe\$eCuRe\$eCuRe\$...
2k views

### 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 ...
779 views

### How the NSA can break trillions of encrypted Web and VPN connections

Based on Diffie-Hellman's negotiation of key exchange, why would it turn out that only a few primes are commonly used? What and who determines the prime? Would it not be safer to use a safe prime? (...
738 views

### Identifying, analyzing, and predicting weak session cookies

To elaborate on this, I'm looking at this from the perspective of a hacker/penetration tester. Many times I have seen web applications that I know have weak cookies. I can tell this because I can ...
1k views

### How easy is it to find a password in a huge text file?

Say that my password is PASSWORD1 I have a 10MB jumbled text file. I hide my password in two parts in the text, between > and < so I can find it myself. Then I put the 2 parts together and add the ...
565 views

### NSA crypto Suite B - historical

I'm looking for information on what NSA suggested for use in commercial systems in past times. 90's and early 2000's. I'm mainly interested in PKI and symmetric cyphers for SSL and file/disk ...
2k views

### Classical Cryptography Tools

I'm wondering if there are any tools out there that can assist in solving classical cipher text. I'm looking into developing some tools such as frequency analysis, transposition tools and so on but ...
1k views

### Is there a method to get plain-text from cipher-text in HMAC SHA-1, given that the key is known?

This is technically not even an attack. We have all the resources at hand, except for the original plain-text. We have the cipher-text (to be converted back to plain-text), as well as the key. The ...
10k views

### The new CCMP attack against WPA/WPA2 PSK

The use of Counter Mode with Cipher Block Chaining Message Authentication Code Protocol (CCMP) for WPA/WPA2 PSK is being attacked. This is a trivial attack (offline brute force) against the initial ...
290 views

### How is a hash's algorithm detected based on the hash?

I was reading an Ars Technica article this morning and came across the following towards the end (emphasis mine): Equation Group included six other hashes in different exploits that remain unknown ...
7k views

### Is it possible to decrypt a SSL/TLS session without doing a MITM-attack?

I'm not talking about decrypting the connection while the SSL/TLS is happening (MITM) but after the connection is closed and I have a pcap file of the entire negotiation/data transfer process. How ...
5k views

### Brute force vs other methods of recovering passwords from shadow file

Do you know any good approach for de-hashing/actually bruteforcing hashed passwords in the shadow file? On various operating systems, any good solutions/methods/programs. Or is it better to upload ...
553 views

### Known plaintext; What cipher is being used here? [closed]

plaintext: CANDY VERY CRANBERRY ciphertext: TXOtWjYhVk 8&O\$4AmSA plaintext: http ciphertext: cZf. plaintext: http ciphertext: r5Hz This is definitely somehow decodable from ciphertext....
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Section 2 of RFC 2104 defines the key used in HMAC should be padded with zero bytes up to the block length of the underlying hash algorithm. Isn't this a potential security vulnerability since any key ...
385 views

### How valid is the concern over narrow pipe hash function designs?

Narrow pipe hash function designs have recently come under fire, particularly in reference to some SHA-3 candidates. Is this criticism valid? Can it be explained more simply than this paper does? I'm ...
316 views

### Is it ever possible to crack an encryption key character by character?

In movies and TV shows, characters are often depicted using devices and applications that are able to determine an encryption key or passcode character by character (or digit by digit). I am a ...
6k 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 ...
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### How can i calculate the number of possible passwords?

I have found a flaw in a site where the password reset feature resets passwords in the following format UpperCaseLetter-Number-LowerCaseLetter-Number-LowerCaseLetter-Number-UpperCaseLetter Eg:...
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### Can key files be brute-forced like passwords?

Let's say you use a program like Truecrypt or Keepass which allows you to have a password + key file. I understand that passwords can be brute-forced/dictionary-attacked but is the same true for key ...
533 views

### Hashed passwords - How many variations of rainbow tables?

First off...I passed the CISSP exam. WOOOO. I had to get that out. GCIH and CEH by Sept. 11' So, while studying for the technical side of things, I see that there are rainbow tables. They are pre-...
395 views

### Remedy for not having filled the disk with random data?

Filling a large HDD with /dev/urandom prior to encryption can be extremely slow (even with netcat, multiple instances in parallel, etc) and for this reason I'm sure a lot of users skip this advice ...
394 views

### is it easier to get the original password if you have multiple hashes of it?

Most users tipically use the same password for multiple applications. Let's say all of these applications hash the password in some way. Would it be easier for an attacker to get the original password ...
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### Cracking DES(Unix)/MD5 ARP

This is a basic example of an Unix Pass Encryption. I have a little Hash of MD5 ARP: user50:\$apr1\$w7YNTrjQ\$0/71H7ze5o9/jCnKLt0mj0 user60:\$apr1\$AIw2h09/\$Ti0TRlU9mDpCGm5zg.ZDP. I need to find the ...
720 views

### Soundness of GRC.com Haystack padding concept [duplicate]

I was wondering how sound is the concept presented by the Gibson Research Corporation (see below if you do not want to follow the link) about simple passwords (= very easy to remember) with the ...
184 views

### Does knowing encrypted information make it easier to find an unknown key?

I'm curious if knowing the exact content of an encrypted message or several messages makes it theoretically any easier to discover the encryption key. Does this speed up a brute force attack in any ...
94 views

### Targeted acoustic keylogging attack prevention

To what level could this be applied to? Could someone record keystrokes on a keyboard and in combination with typing habits start to put together a picture of what the user is typing? If this is ...
2k views

### How does a brute force attack actually determine it has succeeded? [duplicate]

Possible Duplicate: If someone breaks encryption, how do they know they're successful? First off, this is not about cracking hashed passwords. I know that a brute-force or dictionary ...
1k views

### Is AES encryption vulnerable?

I was reading weaknesses in AES encryption. Unfortunately, I have a website that uses AES: Its database is almost entirely AES encrypted. Is there a real threat? Would it be worth to refactor the web ...
451 views

### How to optimize compressed file cracking?

I'm currently doing research on cracking encrypted, compressed files (specifically: uif, zip, 7z, dmg). Looking at all the utilities out there, it seems the time it takes to crack something is ...
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### Klein and PTW wep attack

I'm working on an implementation of Klein's wep attack. For that, I've set up a router with wep encryption and collected 50,000 unique IVs from it. I tried only calculating K[0], meaning - the first ...