|The Open–source PKI Book: A guide to PKIs and Open–source Implementations|
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Having the authentic public keys of each other, users can communicate securely. They can encrypt data and make use of digital signatures. For the part of encryption, public key cryptography is too slow to be used for the transfer of large quantity of data. A symmetric cipher is more suited to this purpose. For this reason, the key for the symmetric cipher is transferred encrypted using public–key cryptography.