Abstract: First data to be sent by a first party to a second party is encrypted using an encryption key string formed using at least a hash value generated using second data and a secret, shared with a trusted party, that serves as identification of the first party. The second data comprises, for example, one or more conditions that serve as identifiers of the second party, and a hash-value element generated by hashing the first data. The encrypted first data and the encryption key string is made available to the second party which forwards the encryption key string to the trusted party with a request for the corresponding decryption key. The trusted party carries out at least one check on the basis of data contained in the encryption key string and, if this at least one check is satisfactory, provides a decryption key to the second party.

Abstract: A trusted authority delegates authority to a device. This delegation of authority is effected by providing a yet-to-be completed chain of public/private cryptographic key pairs linked in a subversion-resistant manner. The chain terminates with a penultimate key pair formed by public/private data, and a link towards an end key pair to be formed by an encryption/decryption key pair of an Identifier-Based Encryption, IBE, scheme. The private data is securely stored in the device for access only by an authorized key-generation process that forms the link to the end key pair and is arranged to provide the IBE decryption key generated using the private data and encryption key. This key generation/provision is normally only effected if at least one condition, for example specified in the encryption key, is satisfied. Such a condition may be one tested against data provided by the trusted authority and stored in the device.