Tag Archives: #ctf

[HackingWeek 2015] [Crypto2] Write Up

Introduction

Bob uses a RSA public key with the public exponent e = 65537 and modulus:

N = 55089599753625499150129246679078411260946554356961748980861372828434789664694269460953507615455541204658984798121874916511031276020889949113155608279765385693784204971246654484161179832345357692487854383961212865469152326807704510472371156179457167612793412416133943976901478047318514990960333355366785001217

The challenge validation key is given by the md5sum of the value of its private key d.

Continue reading [HackingWeek 2015] [Crypto2] Write Up

[HackingWeek 2015] [Crypto3] Write-up

Description

Alice wants to use the ECDSA signature algorithm.
For this, she chooses to use the elliptic curve equation E where y2 = x3 – x, defined on the finite field with q elements, Fq, with q = 134747661567386867366256408824228742802669457 .

She chose P as a base point of order N = 2902021510595963727029 with:
P = (18185174461194872234733581786593019886770620, 74952280828346465277451545812645059041440154)

Then, she chooses as secret signature key a random integer d with 1<d<N.
The public key is the point Q=d⊗P where ⊗ is the scalar multiplication on the elliptic curve E.

The value of Q is:
Q=(76468233972358960368422190121977870066985660, 33884872380845276447083435959215308764231090)

The validation key is given by the value of d.

Continue reading [HackingWeek 2015] [Crypto3] Write-up