B2B Integration : A Practical Guide to Collaborative E-commerce

Internet Security 297
communication to the person who signed it. It also guarantees that the
message was not modified since it left the sender. Digital signatures
rely on public key systems.
Creating a digital signature
A digital signature is typically created using what is known as a hash
function. A hash function is an algorithm that maps values from a large
domain into a much smaller range. In other words, if we have a typical
message, which consists of many thousands of bits, the hash algorithm
can produce a 'digest' of it, which would be about a hundred bits in
length. Also, it would ensure that even if one bit is changed in the
message, the digest produced would be different. This 'message digest'
is encrypted using the sender's private key (usually RSA encryption)
and the result is called the digital signature (see Figure 10.5).
The digital signature is attached to the message file and the combined
message is encrypted with the receiver's public key (see Figure 10.6).
Receiver's
Public Key
Message
Hash
Function
Message
PMWMS?
Sender's Private
Key
Message
Digest
Digital
Signature
Figure 10.5. — Creating a digital signature
Digital
Signature
Signed and
Encrypted
Secured Message
Figure 10.6.
signature
Encryption using digital