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MIX & MASH - InCTF Internationals 2020

v3ct0r
2020-08-14
Crypto

tl;dr

  • Extract higher bits of secret using input manipulation
  • Extract lower bits of secret using the highers bits and input manipulation
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InCTFi

Faulty LFSR - InCTF Internationals 2020

ph03n1x
2020-08-02
Crypto / LFSR

tl;dr

  1. Find the co-relation between variables in the LFSR equation
    1. d == out (75%)
    2. a == b (75%)
    3. c^d == out (75%)
    4. (d!= out) => (c==1) always
  2. Solve for the seed using 2000 output bits
  3. Try out which among the four possible combinations decrypt the flag
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InCTFi LFSR Correlation attack

PRetty stroNG - InCTF Internationals 2019

v3ct0r
2019-10-01
Crypto / PRNG

Intended solution of PRetty stroNG challenge from InCTF Internationals 2019

tl;dr

  • Recover sample outputs from PRNG
  • reverse wrapper function
  • find seed from outputs
  • get the flag
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InCTFi PRNG DLP ElGamal

waRSAw - InCTF Internationals 2019

s0rc3r3r
2019-09-29
Crypto / PubKey-Enc

Intended solution of waRSAw challenge from InCTF Internationals 2019

tl;dr variant of LSB Oracle Attack on unpadded RSA

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InCTFi NumberTheory PublicKeyCrypto RSA

Halloween Party - ASIS CTF Quals 2019

s0rc3r3r
2019-04-23
Crypto / Elliptic-Curves

tl;dr

  1. Find Elliptic Curve parameters from given points on the curve
  2. Find x-coordinate of 2*P, given y-coordinate of 2*P
  3. Invert 2 over mod (P.order()) and multiply the result with 2*P to get P
  4. Submit ASIS{P.x} as the flag
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EZDSA - MidnightSun CTF Quals 2019

s0rc3r3r
2019-04-09
Crypto / Digital-Signatures

Full solution of EZDSA challenge from MidnightSun CTF Quals 2019.

tl;dr retrieving key using Euler’s Criterion to break signature authentication

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Euler NumberTheory PublicKeyCrypto

Blind - Volga CTF Qualifiers 2019

s0rc3r3r
2019-03-31
Crypto / Digital-Signatures

tl;dr solving RSA Digital Signature using it’s homomorphic property:

  1. Calculate the signature of factors of message M to be signed, separately
  2. Combine them by multiplication over modulus to get the signature of M
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Reasonably Suspicious Acronym - Teaser CONFidence 2019

s0rc3r3r
2019-03-18
Crypto / PubKey-Enc

tl;dr Coppersmith’s Attack to recover RSA primes

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RSA Coppersmith

Bro do you even Lift - Teaser CONFidence CTF 2019

v4d3r
2019-03-18
Crypto

tl;dr

  1. Find roots in a polynomial ring over $ mod;p $
  2. Use Hensel’s Lifting lemma to find roots over $ mod;p^k $
Read More
PolynomialRing HenselLifting

Count me in - Teaser CONFidence CTF 2019

v3ct0r
2019-03-18
Crypto / Block-Ciphers

tl;dr Known plaintext attack on a multithreaded AES-CTR

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AES-CTR

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