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Today’s secure devices are mainly used for storage and processing of confidential data. Current products provide hardware and software secure solutions for civil and online identification, telecommunication, healthcare, banking, pay-TV, access control for restricted systems or areas, e-government... Tomorrow, they will include decision making capabilities for machine to machine applications. 20 billion of secure devices are forecasted in 2020 (4 billion in 2007) [Eurosmart, 2007]. Due to their applications, secure devices must be designed so that they can guarantee high levels of dependability and quality. But in addition to usual dependability features (reliability, availability, safety, robustness to environmental conditions), we also expect that they have the ability to protect information against unauthorized access and intentional misuse. The digital security mechanisms involved in such devices rely on various principles: secrecy of design and implementation, ciphering operations for encryption/decryption of confidential data, and hardware and software countermeasures for attack detection or tolerance. Encryption is the process of transforming data in order to make it unreadable to anyone except those possessing the decryption key. Encryption can be symmetric or asymmetric. In symmetric encryption, a sender and a recipient share the same secret key, which is used for both encryption of plaintexts and decryptions of corresponding cipher texts. Conversely, the asymmetric algorithms use different keys for encryption and decryption. A sender S communicate his/her public key to all recipients R; messages encrypted with that public key by any R can only be decrypted by the sender S using his/her corresponding private key. The symmetric and asymmetric algorithms are generally public, while the secret and private keys are kept secret. Symmetric encryption is fast but senders and recipients need to define a “secure” key exchange process prior to start communication. Asymmetric encryption can be used for exchanging this secret key at the beginning of a communication, and then a symmetric-key algorithm using that secret key can be used for fast encryption during the remainder of the communication. The section 2 details the Advanced Encryption Standard 9 |
