• ### The Weakest Link in Many Cryptosystems - Part 2 of 2

26. November 2021
• ### Signing in the Cloud

08. January 2015
• ### The Weakest Link in Many Cryptosystems – Part 1 of 2

13. November 2012
• ### Digital Rights Management Protection

15. September 2011

# Cryptomathic Blog

## Peter Landrock

Peter Landrock (born August 20, 1948 in Horsens ) is a Danish cryptographer and mathematician. He is known for his contributions to data encryption methods and codes. Peter has been active since the 1970s as research scientist and faculty member for Cambridge University and the University of Aarhus and others, and was active for Microsoft and Cryptomathic. He has been visiting professor at Oxford University, Leuven University and Princeton University. (source: Wikipedia)
The Weakest Link in Many Cryptosystems - Part 2 of 2

### RSA, a short recap

In a public key scheme, and for the sake of simplicity, assume a public scheme based on encryption-decryption (as opposed to e.g. DSA, the Digital Signature Algorithm, where the digital signature generated by the secret key is verified to satisfy a mathematic equation using the corresponding public key), you have two mathematical functions, called keys, the secret key S and the public key P and one is the inverse of the other, e.g. on a message m, P(S(m)) = S(P(m)) = m. RSA is the only widely used public key encryption scheme, constructed as follows: Generate two primes p and q of a fixed bit length, say 512 bits using a sufficiently random input. Denote the product by n, also known as the modulus. Now chose an appropriate so-called public exponent e. It must be prime to p - 1 and q - 1 (and there is no point in choosing it larger than φ(n) := (p - 1)(q - 1), as always, mφ(n) = 1 mod n - see below). There are computation advantages in choosing e small, such as 3, 17 or 65537 = 216 + 1, also known as the 4th Fermat prime. By running an extended version of Euclid's algorithm, which normal outputs the smallest common divisor of two numbers a and b, you can relatively easily find a number d such that for some number a, e∙d -a∙φ(n) = 1 modn. In the following, we just write ab rather than a∙b.

Signing in the Cloud

## Introduction

What is driving Electronic Commerce and e-Government solutions? The answer is simple: useful applications and user-friendly yet secure solutions that can deliver operational cost savings. Smartcards, used for providing digital signatures for Electronic Commerce (EC), never caught on in any significant volume because there are very few smartcard readers around, making such solutions very expensive.

The Weakest Link in Many Cryptosystems – Part 1 of 2

### Introduction

It is well-known and appreciated by most users - even if often ignored(!) - that if you choose a weak password, you are exposing yourself to various risks. Whether your password is used for encryption of confidential data or just for access control doesn't really matter, so let's assume for a minute that it is actually used to encrypt your data - or perhaps to encrypt a key that is used to encrypt your data. The situation you are in is that

Digital Rights Management Protection

### Digital Rights Management Protection

In 2004, Intel, Nokia, Panasonic, and Samsung, announced plans for a licensing and compliance framework called Content Management License Administrator (CMLA) (see www.cm-la.com). This body was formed to address necessary business concerns and enable rapid delivery of high-quality digital files to mobile handsets and other devices that deploy Open Mobile Alliance (OMA).