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A related measure is the base-2 logarithm of the number of guesses needed to find the password with certainty, which is commonly referred to as the "bits of entropy". [9] A password with 42 bits of entropy would be as strong as a string of 42 bits chosen randomly, for example by a fair coin toss.
The above calculations of the Diceware algorithm's entropy assume that, as recommended by Diceware's author, each word is separated by a space. If, instead, words are simply concatenated, the calculated entropy is slightly reduced due to redundancy; for example, the three-word Diceware phrases "in put clammy" and "input clam my" become ...
In cryptography, key stretching techniques are used to make a possibly weak key, typically a password or passphrase, more secure against a brute-force attack by increasing the resources (time and possibly space) it takes to test each possible key. Passwords or passphrases created by humans are often short or predictable enough to allow password ...
The salt and hash are then stored in the database. To later test if a password a user enters is correct, the same process can be performed on it (appending that user's salt to the password and calculating the resultant hash): if the result does not match the stored hash, it could not have been the correct password that was entered.
Example of a Key Derivation Function chain as used in the Signal Protocol.The output of one KDF function is the input to the next KDF function in the chain. In cryptography, a key derivation function (KDF) is a cryptographic algorithm that derives one or more secret keys from a secret value such as a master key, a password, or a passphrase using a pseudorandom function (which typically uses a ...
A main encryption/decryption key is derived from user's password by PBKDF2 function. [2] Particular data binary large objects can be encrypted in a way that salt is added and/or an external user-prompted password (aka "Strong Key Protection") is required. The use of a salt is a per-implementation option – i.e. under the control of the ...
Or in another way; it raises minimum-entropy value of the password set. At the same time it excludes only low-entropy sets (e.g. all lower or all upper case) so the maximum-entropy value passwords are unaffected. The overall result is to force an increase in the median/mean entropy of the password pool.
There are several "pools" of entropy; each entropy source distributes its alleged entropy evenly over the pools; and (here is the key idea) on the nth reseeding of the generator, pool k is used only if n is a multiple of 2 k. Thus, the kth pool is used only 1/2 k of the time. Higher-numbered pools, in other words, (1) contribute to reseedings ...