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Special Forums Cybersecurity Password-based challenge-response Post 302101259 by heroine on Friday 29th of December 2006 09:04:00 PM
Old 12-29-2006
Password-based challenge-response

Hello all,

I have this question, hope to get some guidance...

Fora simple password-based challenge-response protocol between a user A
and a server S, where Pa is A's password, n is a random nonce generated
by the server, and h is a known cryptographic hash function.

1. S -> A: E(Pa,n)
2. A -> S: E(Pa,h(n))

How to show that this protocol is vulnerable to an off-line password
guessing attack? and how would the attack take place ?. Under which
circumstances would the vulnerability not be a problem?

thanks for reading...
cheers.
 

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RADCRYPT(8)						      System Manager's Manual						       RADCRYPT(8)

NAME
radcrypt - generate password hash for use with radius, or validates a password hash SYNOPSIS
radcrypt [-d|--des] [-m|--md5] [-c|--check] plaintext_password [hashed_password] DESCRIPTION
radcrypt generates a hashed digest of a plaintext password, or can validate if a password hash matches a plaintext password. DES and MD5 hashes are currently supported. When generating a password hash a random salt is generated and applied. A hashed password can be validated by specifying -c or --check and passing hashed_password after plaintext_password on the command line. In this case hashed_password will be checked to see if it matches plaintext_password. If so "Password OK" will be printed and the exit sta- tus will be 1, otherwise "Password BAD" will be printed and exit status will be 0 (Note this is the opposite of a normal successful shell status). OPTIONS
-d --des Use a DES (Data Encryption Standard) hash (default). Ignored if performing a password check. -m --md5 Use a MD5 (Message Digest 5) hash. Ignored if performing a password check. -c --check Perform a validation check on a password hash to verify if it matches the plantext password. EXAMPLES
$ radcrypt foobar HaX0xn7Qy650Q $ radcrypt -c foobar HaX0xn7Qy650Q Password OK SEE ALSO
radiusd(8), crypt(3) AUTHORS
Miquel van Smoorenburg <miquels@cistron-office.nl> RADCRYPT(8)
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