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Trail: Security in Java 2 SDK 1.2

## Lesson: Exchanging Files

> If you want to electronically send an important document, such as a contract, to someone else, it is a good idea to digitally "sign" the document, so that the recipient has a way of checking that the document indeed came from you and was not altered in transit.

> This lesson illustrates the use of security-related tools for the exchange of an important document, in this case a contract. You first pretend that you are the contract sender, Stan Smith. This lesson shows the steps Stan would use to put the contract in a JAR file, sign it, and export the public key certificate for the public key corresponding to the private key used to sign the JAR file.

> Then you pretend that you are Ruth, who has received the signed JAR file and the certificate. You'll use `keytool` to import the certificate into Ruth's keystore in an entry aliased by `stan`, and the `jarsigner` tool to verify the signature.

> For further information about digital signatures, certificates, keystores, and the tools, see the API and Tools Use for Secure Code and File Exchanges lesson.

> > Note: The commands executed in this lesson are assumed to all be done from within the same directory.

> Here are the steps:

> - Steps for the Contract Sender

> - Steps for the Contract Receiver

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