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seen Feb 24 at 8:25

Feb
6
comment Securely send public key from client to server in RSA?
The protocol is vulnerable to an attack where the attacker can make both the server and the client believe they have exchanged a correct session key while the attacker has exchanged another one with the server and can send him correct messages if he knows the protocol. You need to add identifiers and any kind of authentication to your messages to prevent this attack.
Feb
5
comment Securely send public key from client to server in RSA?
If each client knows (or can trust) the server's public key they can establish a secure communication channel and exchange the client's certificate by using TLS. If you also want the client to authenticate to the server you need to be sure the certificate is authentic - this requires a PKI!
Apr
4
awarded  Commentator
Apr
4
comment How can mega store my login details and still be secure?
Mega uses neither MD5 nor SHA*! They implemented a self-made hash-function that can be found in this file (eu.static.mega.co.nz/crypto_23.js) at line 97 (function prepare_key). The function encrypts a fixed string with the password as the key for fixed iterations. Unfortunately, I cannot say anything about the security of this construction...
Mar
18
comment Simple example for CP-ABE (Ciphertext policy attribute-based encryption)
Spontaneously, I would say that your pairing definition is correct, but cannot be applied to CP-ABE. The group $\mathbb{Z}_p$ has order $p-1$, but CP-ABE requires a group of prime order and I think a subgroup of prime order would not be sufficient. Of course, elliptic curves and Miller's algorithm are very difficult to calculate in a toy example, but I think you need to...
Mar
12
comment Encrypting many small messages (log-lines)
If you implement it like this, I think there will be another problem: How do the logging sub systems receive the "reused-key"? I think the intent of public key cryptography in this scenario should be that these systems only need the public key to add log messages.
Mar
7
comment Exponentiation In PBC library
Your code above does not show the most important part, where you initialize the elements. The ring $Z_r$ (or sometimes calls $Z_n$) is designed to calculate with exponents. So you have to use the function element_init_Zr() for b and bi and then you can calculate the inverse with element_invert(bi,b).
Mar
4
comment Simple example for CP-ABE (Ciphertext policy attribute-based encryption)
Your definition of the pairing $e(X,Y)=g^{XY} \mod p$ with $p=13$ and $g=7$ does not hold the biliniarity property, because $e(7^2,7^3) \neq e(7,7^2)^3 \neq e(7,7^3)^2 \neq e(7,7^6) \neq e(7,7)^6$. All these expressions should be equal, but if you evaluate the first two expressions you get $e(7^2,7^3) = 7^{10\cdot5} = 10$ and $e(7,7^2)^3 = (7^{7\cdot10})^3 = 4^3 = 12$. To my knowledge, there are no pairings for finite fields and you need to use elliptic curves.
Mar
1
answered Simple example for CP-ABE (Ciphertext policy attribute-based encryption)
Nov
3
awarded  Enthusiast
Oct
31
comment Distinguish messages
This was only an example and there will be no secure encryption scheme that stretches the ciphertext very much. BUT if you really get an encryption scheme that stretches the ciphertext there must be any step in the algorithm description where the length is defined and at this point you can attack.
Oct
31
awarded  Editor
Oct
31
revised Distinguish messages
edited body
Oct
31
comment Distinguish messages
Yes, of course. I will edit my post.
Oct
30
answered Distinguish messages
Oct
30
comment Can ElGamal encryption and ElGamal signatures be used together sharing the same key-pairs?
Maybe the paper Digital Signcryption or How to Achieve Cost(Signature & Encryption) << Cost(Signature) + Cost(Encryption) from Y. Zheng can be interesting for you. He introduced an ElGamal signcryption sheme with only a single key-pair.
Oct
27
comment Would this simple encrypted chat program be feasible using One Time Pads?
Yes, but in the protocol description you have to make sure that the keys get deleted directly after usage. Everything in context of the chat GUI is not part of the cryptographic protocol. The GUI handles only the plaintext messages and decides when it deletes them.
Oct
26
answered Would this simple encrypted chat program be feasible using One Time Pads?
Oct
23
awarded  Supporter
Oct
9
answered Perfect security definitions