Not So Random

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PRNG “Randomness” • These numbers aren’t actually random at all • PRNGs generate a sequence of numbers in order • Sequence is repeatable; two PRNGs with same internal state will generate same sequence of numbers • “Random” enough to pass statistical randomness tests Not So Random
PRNG Seeds, States and Periods 1. Seed • Initial value used to determine “starting” point of a PRNG; initial state 2. State • Current internal properties of the PRNG • Makes a PRNG deterministic; next (and previous) values can be determined if state known 3. Period • Length of all the possible outputs from a PRNG before output is repeated • e.g. Mersenne Twister period of 2^19937-1 • Large period value =/= security Not So Random
Page 1 and 2: Not So Random Exploiting Unsafe Ran
Page 3 and 4: Talk Overview 1. Theory: • Why?
Page 5 and 6: Why do we need random numbers? •
Page 7 and 8: Random numbers in Web Applications
Page 9 and 10: Concept of Randomness • define: r
Page 11 and 12: PRNG PRNG r = random.Random() Not S
Page 13 and 14: PRNG 16768642083820545282 323536147
Page 15: PRNG PRNG 16768642083820545282 3235
Page 19 and 20: PRNG Seeds and States Seed (/dev/ur
Page 31 and 32: CSPRNG vs PRNG 1. Non-Deterministic
Page 33 and 34: Language Examples Language Method P
Page 35 and 36: Internals Glance public Random(int
Page 37 and 38: Exploitation Theory • Want to obt
Page 39 and 40: Exploitation Theory Target PRNG Out
Page 41 and 42: Exploitation Theory Target PRNG Out
Page 43 and 44: Exploitation Theory Target PRNG Obt
Page 45 and 46: Exploitation Theory Our PRNG Obtain
Page 47 and 48: Untwister Brute Force Algorithm 101
Page 65 and 66: Demos 1. Brute Force • PHP mt_ran
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Overview - Brute Force 1. Generate
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Brute Force - Source class ResetPas
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PHP mt_rand()- Exploitation • Rec
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PHP mt_rand()- Exploitation • Tar
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PHP mt_rand()- Exploitation Theory
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PHP mt_rand() - Untwister uint32_t
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PHP mt_rand()- Exploitation root@ka
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PHP mt_rand()- Exploitation class R
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5. Generate a number of tokens usin
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6. Attempt tokens against applicati
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PHP mt_rand()- Exploitation “To r
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Demos 1. Brute Force • PHP mt_ran
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Overview - Brute Force Bounded Call
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Brute Force Bounded Call - Source c
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PHP mt_rand(0,61)- Exploitation •
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PHP mt_rand(0,61)- Exploitation •
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Exploitation Theory Target PRNG Obt
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PHP mt_rand(0,61)- Decoder #!/usr/b
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PHP mt_rand(0,61)- Exploitation # p
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PHP Bounded mt_rand() Constructor
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PHP Bounded mt_rand() - Patched Unt
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PHP mt_rand(0,61)- Exploitation roo
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4. Seed new PRNG with obtained seed
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PHP mt_rand(0,61)- Exploitation
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PHP mt_rand(0,61)- Exploitation # p
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PHP mt_rand(0,61)- Exploitation Not
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Exploitation Theory Our PRNG Obtain
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Overview - Weak Seeds 1. Generate a
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Weak Seeds - Source public class Re
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.NET System.Random() Constructor
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.NET System.Random()- Exploitation
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Exploitation Theory Observed PRNG O
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System.Random() Constructor • .NE
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System.Random() Untwister Patch int
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5. Attempt tokens against applicati
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Exploitation Theory Observed PRNG O
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Practical Exploitation - Tips • L
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Mitigations Need a truly random num
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Developers, Developers, Developers
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Links / Further Reading • https:/
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Not So Random

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