All Questions

252 views

Is it OK to use a data-encryption key for key wrapping, too?

Our industry (area of cheap networked devices) has a standard that defines the usage of keys for both authentication and encryption using EAX mode of AES. This standard does not define key management, ...
999 views

Self-expiring symmetric keys, or: cryptography in absence of secure deletion

I can encrypt some data D using a random symmetric key K, obtaining a ciphertext C, and then encrypt K with my public key Pub and obtain H. So far so good: I can only decrypt C if I have H and my ...
2k views

Can Elgamal be made additively homomorphic and how could it be used for E-voting?

Elgamal is a cryptosystem that is homomorphic over multiplication. How can I convert it to an additive homomorphic cryptosystem? How can I use this additive homomorphic Elgamal cryptosystem for E-...
768 views

Can I make a cipher (ex: Vigenère) harder to break?

The Vigenère cipher can relatively easy be broken when the key size is small compared to the size of the message. One first finds the length of the key, and then uses frequency analysis to actually ...
317 views

Detect tampering of data

I have the following problem: There are $n$ users and each users fills in three data points per day, this are three integers between say $-10$ and $10$. I have access to the database and hence I am ...
4k views

How do ciphers change plaintext into numeric digits for computing?

For example, in RSA, we use this for encryption: $ciphertext = (m^e \mod n)$ and for decryption. If our message is "hello world", then what number do we have to ...
17k views

What is the effect of the different AES key lengths?

How does a changing key length affects the ciphertext, not only in case of AES, but in general? I know that the key spaces become much larger and the number of rounds in case of AES changes, but is ...
2k views

HRNG for One Time Pad

I have just advanced to the last grade of high school (in Denmark). In this year, we all get to do one big project, where we can build/invent/create whatever we want to "solve a problem". As I study ...
17k views

Why is padding used for RSA encryption given that it is not a block cipher?

In AES we use some padded bytes at end of message to fit 128/256 byte blocks. But as RSA is not a block cipher why is padding used? Can the message size be any byte length (is the encrypting agent ...
352 views

Security considerations for partially shared password databases

Programs like KeyPass and 1Password store password database files encrypted by a single password. If someone knows the protecting password ("Vault Key"), they can read the entire database ("secrets"). ...
360 views

Blowfish Encryptions in Bcrypt hashing algorithm

I am trying to understand the ExpandKey function used in the bcrypt hashing algorithm. As per the documentation of bcrypt hashing algorithm on USENIX here: http://static.usenix.org/event/usenix99/...
2k views

Difference in one time key and one time pad and many time key

These terms are confusing me. One time pad is when you use one key for one message. That is what One time key is. Secondly, what is the connection of many time key, can i use one time pad many times,...
401 views

Why can't Homomorphic encryption schemes support algorithms with conditions/branching?

If it isn't already apparent from the title of my question, i should make clear that I have only a very basic understanding of homomorphic encryption. I would like to know why homomorphic encryption ...
2k views

Is it possible to pick your Ed25519 public key?

Is it possible to generate an Ed25519 keypair that has a very similar public key as another keypair (fooling a casual visual comparison) or is this as hard as solving one of SHA-512 or the discrete ...
897 views

RSA 1024bit decryption performance

i want to know how many RSA 1024 bit long key decryption can a regular pentium4 computer do per second ? how to calculate RSA performance and determine its remaining time ?
248 views

Zero Knowledge auth schemes with weak secret

In Zero Knowledge auth schemes the public DH factor of each peer is encrypted with a potentially weak pre-shared secret and the resulting ciphertexts are exchanged over an insecure channel. Why is no ...