Abstract: There is described an electronic data communication system in which encrypted mail messages for a recipient are sent in two parts: message data encrypted by a symmetric encryption algorithm using a session key and session key data encrypted by an asymmetric encryption algorithm using a public key associated with the recipient. If the recipient uses a webmail service to access the encrypted electronic mail message, the encrypted session key data is sent to a trusted third party server which has access to the private key of the user. The trusted third party server decrypts the encrypted session key using the private key of the user, and then sends the decrypted session key to a remote network device for decryption of the encrypted message.

Abstract: There is described a key server which is connected to a local area network, and an encryption authority transfers private keys for clients of the local area network to the key server. In an embodiment, the key server encrypts outgoing emails using public keys for the recipients and decrypts internal emails using private keys for the recipients. In another embodiment, the clients of the local area network download their respective private keys from the key server so that encryption operations may be performed by client software.

Abstract: There is described an electronic data communication system in which encrypted mail messages for a recipient are sent in two parts: message data encrypted by a symmetric encryption algorithm using a session key and session key data encrypted by an asymmetric encryption algorithm using a public key associated with the recipient. If the recipient uses a webmail service to access the encrypted electronic mail message, the encrypted session key data is sent to a trusted third party server which has access to the private key of the user. The trusted third party server decrypts the encrypted session key using the private key of the user, and then sends the decrypted session key to a remote network device for decryption of the encrypted message. In this way, although the trusted third party has access to the private key of the user, the trusted third party does not have access to any decrypted message.

Abstract: There is described a key server which is connected to a local area network, and an encryption authority transfers private keys for clients of the local area network to the key server. In an embodiment, the key server encrypts outgoing emails using public keys for the recipients and decrypts internal emails using private keys for the recipients. In another embodiment, the clients of the local area network download their respective private keys from the key server so that encryption operations may be performed by client software.

Abstract: There is described an electronic mail messaging system in which a plurality of user computers are connected to a mail registration server via the Internet. The mail registration server stores plural sets of decryption data, each set being required to decrypt a corresponding encrypted electronic mail message. Following receipt of an encrypted electronic mail message, a user computer communicates with the mailed registration server to effect decryption of the encrypted electronic mail message using the corresponding decryption data stored by the mail registration server. In this way, the accessing of the electronic mail message can be monitored by the mail registration server.

Abstract: There is described an electronic data communication system in which encrypted mail messages for a recipient are sent in two parts: message data encrypted by a symmetric encryption algorithm using a session key and session key data encrypted by an asymmetric encryption algorithm using a public key associated with the recipient. If the recipient uses a webmail service to access the encrypted electronic mail message, the encrypted session key data is sent to a trusted third party server which has access to the private key of the user. The trusted third party server decrypts the encrypted session key using the private key of the user, and then sends the decrypted session key to a remote network device for decryption of the encrypted message. In this way, although the trusted third party has access to the private key of the user, the trusted third party does not have access to any decrypted message.

Abstract: Video signals are compressed by removing complementary sets of pixels from alternate frames. In one embodiment, the removed pixels are determined to be static or moving, from an analysis of the temporally and spatially neighbouring remaining pixels and reconstructed by processes selected in dependence on whether they are static or moving. In another embodiment, the selection or combination of temporally and/or spatially neighbouring pixels required to reconstruct removed pixels is embedded in the data code of remaining pixels.