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Practical Web Technologies by V. Lau, P. K. Yuen

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19.4. MD and digital signatures

The MD algorithm (or process) is a basic tool in advanced cryptography and security, and can be used to encrypt a password. More importantly it can produce the so-called digital signature in many applications related to the Internet and Web. If you want to sign a document or file just like you sign a paper document so that no one can alter it afterward, you need to use MD. The basic idea is simple and can proceeds as follows:

  • Run your document or file through the MD or md5() function. This would produce a fixed length MD string similar to the encrypted password representing the signature of the document.

  • Send your document and the signature to the intended recipient by email or other transmission method.

  • The recipient ...

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