5.3. Digital Signatures

PK encryption can be used for digitally signing an electronic document in a way that allows for later validation for authenticity [5]. We explain here, with the help of Fig. 5.3, how digital signatures work.

Figure 5.3. Digital Signatures.

Suppose that A wants to send a message Msg to B. The following steps are followed by A before sending the message.

1.
A generates a fixed size string, called the message digest (MD), by applying a one-way hash function h to the message Msg. So MD = h (Msg). For a hash function to be useful for digital signatures, it must have the following properties:
  • it should be easy to compute

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