Hash Based Key Stretching
A collision prone simple key stretching method:
key = hash(password) for 1 to 65536 do key = hash(key)A better simple key stretching method. ("+" denotes the operation of concatenation):
key = "" for 1 to 65536 do key = hash(key + password)Even better method with a salt:
key = "" for 1 to 65536 do key = hash(key + password + salt)Many libraries provide functions which perform key stretching as part of their function; see crypt(3) for an example. Note that PBKDF2 is for generating an encryption key from a password, and not necessarily for password authentication. PBKDF2 can be used for both if the number of output bits is less than or equal to the internal hashing algorithm used in PBKDF2 which is usually SHA-1 (160 bits) or used as an encryption key to encrypt static data.
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Famous quotes containing the words based, key and/or stretching:
“That’s my problem, chaplain: I’m yellow. PFC Bernstein—plumb, fat coward. Hey, can you get a Section 8 for being yellow?”
—James Poe, U.S. screenwriter, and Based On Play. Robert Aldrich. Bernstein (Robert Strauss)
“All meanings, we know, depend on the key of interpretation.”
—George Eliot [Mary Ann (or Marian)
“There was now no road further, the river being the only highway, and but half a dozen log huts, confined to its banks, to be met with for thirty miles. On either hand, and beyond, was a wholly uninhabited wilderness, stretching to Canada.”
—Henry David Thoreau (1817–1862)