## Login - Fword CTF 2021

tl;dr

• use RSA properties to recover $q$ and get $p$ and therefore $N= p*q$.
• sign the message given, and get the flag.

## Encrypted Operations - InCTF Internationals 2021

tl;dr

• Multiplying the middle element of 3x3 matrix with 9 gets thesum of all elements.
• Adding the least element of 5x4 matrix with the larget and multiplying this result by 10 gets the sum of all elements.
• multiplying any row with 2000 and subtrating that number by 2 will get you the sum.
• Remaing two rows can be filled with the result of subtracting 9 from each digit of a corresponding row .

## Tabula Recta - InCTF Internationals 2021

Official writeup of Crypto challenge “Tabula Recta” from InCTFi 2021

tl;dr

• Retrive first few bytes of table through Matrix calculations, then find which special b-exact key is used.

## MIX & MASH - InCTF Internationals 2020

tl;dr

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

## Faulty LFSR - InCTF Internationals 2020

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

## PRetty stroNG - InCTF Internationals 2019

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

## waRSAw - InCTF Internationals 2019

Intended solution of waRSAw challenge from InCTF Internationals 2019

tl;dr variant of LSB Oracle Attack on unpadded RSA

## Halloween Party - ASIS CTF Quals 2019

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

## EZDSA - MidnightSun CTF Quals 2019

Full solution of EZDSA challenge from MidnightSun CTF Quals 2019.

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

## Blind - Volga CTF Qualifiers 2019

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