tl;dr

• use hash extension to bypass password check on login.
• use RSA properties to recover $q$ and get $p$ and therefore $N= p*q$.
• sign the message given, and get the flag.

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 .

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.

tl;dr

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

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

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

Intended solution of waRSAw challenge from InCTF Internationals 2019

tl;dr variant of LSB Oracle Attack on unpadded RSA

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

Full solution of EZDSA challenge from MidnightSun CTF Quals 2019.

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

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