One-Way Compression
Data and its fingerprint are a functionally unique pair.
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Besides being very fast– |
| 2 protections offered |
| 1. can't recover original doc |
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←from fingerprint |
| 2. can't find other data to make same fingerprint | ||
Encrypt Many Files uses 1. to disguise clear file name.
More about 1. (preImage) & 2. (collision) protections ↓ Learn More
Avalanche Effect
Even smallest possible change makes a big change in fingerprint.
Try it yourself. . . hash and digest are other names for fingerprint
Hash: '00' (MD-5) result → 'b4b147 ...'
Try to make a message that hashes to→ 'b4b...+anything
Probability says about (16*16*16)/2 tries; –so you'll probably give up.
00 hashes to –b4b147bc522828731f1a016bfa72c073–
it'll take about (16*16*16..32 times)/2 = (1632)/2 = 2 128/2 tries
much, much too many tries, even the the worlds best computers!
(MD-5 is not used in new applications; but is still used to verify authenticity.)
For instance
Fingerprint data (or software) & save copy before it's stored in cloud.
Fingerprint cloud data and match it against saved copy
—ensures cloud data hasn't been modified.
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saved fingerprint must = | |
| fingerprint of downloaded data |
+
=
signed fingerprint (e.g.MAC, HMAC)
1-wayness, collision resistance, birthday attack,...
| → |
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Fingerprints |
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Chapter 7, 13, 14 |
Crypto experts @ crypto.stackexchange on 3 hash properties
(explains where MD-5 & SHA-1 can be safely used)