tl;dr

• This challenge revolves around a hidden power_tower_mod function.
• To obtain the flag, we implement the function ourselves, apply Hensel lifting, collide a CMAC, decrypt an RSA ciphertext and finally solve a subset sum problem.

tl;dr

• ECDSA signing server with biased nonce
• Exploitation by modelling a EHNP instance and using z3 Solver for breaking Mersenne Twister

tl;dr

• Timing-based attack on the double-and-add algorithm to recover secret value d
• Predict pseudo-random value using the NSA backdoor on Dual_EC_DRBG

tl;dr

• CTR bit-flipping attack along with CRC recomputation

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