The key management techniques that we’ve discussed so far are ideally suited to managing asymmetric keys. In fact, although we’ve mentioned that the keystore can hold secret keys, there are some problems with doing so.
When we discussed public and private key pairs, we talked about the bootstrapping issue involved with key distribution: the problem of obtaining the public key of a trusted certificate authority. In the case of key pairs, keeping the private key secret is of paramount importance. Anyone with access to the private key will be able to sign documents as the owner of the private key; he will also be able to decrypt data that is intended for the owner of the private key. Keeping the private key secret is made easier because both parties involved in the cryptographic transfer do not need to use it.
With symmetric keys, however, the bootstrapping issue is even harder to solve because both parties need access to the same key. The question then becomes how this key can be transmitted securely between the two parties in such a way that only those parties have access to the key.
One technique to do this is to use traditional (i.e., nonelectronic) means to distribute the key. The key could be put onto a floppy disk, for example, then mailed or otherwise distributed to the parties involved in the encryption. Or the key could be distributed in paper format, requiring the recipient of the key to type in the long string of hex digits.
Another technique is ...