Keys can be signed like every other file to guarantee their authenticity and integrity. If you are absolutely sure an imported key belongs to the individual specified as the owner, express your trust in the authenticity of the key with your signature.

	Establishing a Web of Trust
Encrypted communication is only secure to the extent that you can positively associate public keys in circulation with the specified user. By cross-checking and signing these keys, you contribute to the establishment of a Web of Trust. For these reasons, make really sure you only sign keys you personally checked.

Select the key to sign in the key list. Select Keys+Sign Keys. In the following dialog, designate the private key to use for the signature. An alert reminds you to check the authenticity of this key before signing it. If you have performed this check, click Continue and enter the password for the selected private key in the next step. Other users can now check the signature by means of your public key.

Normally, you are asked by the corresponding program whether you trust the key, or rather, whether you assume it is really used by its authorized owner. This happens each time a message needs to be decrypted or a signature has to be checked. To avoid this, edit the trust level of the newly imported key. By default, the newly imported key is listed in a white box, meaning that no concrete value has been assigned for the trust level. To trust a key, do the following:

The lower the trust level is, the less you trust the signer of the key to have checked the true identity of the keys signed. You may be entirely sure about the signer's identity, but he may not check other people's identities properly before signing their keys. Therefore, you could still trust him and his own key, but assign lower trust levels to the keys signed by him. Notice that the trust level does not trigger any automatic actions by KGpg.