symmetric-enc - Contents 1 Asymmetric E c y t o :E o u i n...

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CryptoBytes V O L U M E 2 , N U M B E R 1 S P R I N G 1 9 9 6 CRYPTOGRAPHIC RSA LABORATORIES RESEARCH AND CONSULTATION R S A L A B O R A T O R I E S ’ The technical newsletter of RSA Laboratories, a division of RSA Data Security, Inc. Contents 1 Asymmetric Encryption: Evolution and Enhancements 2 Editor's Note 7 PayWord and MicroMint: Two Simple Micropayment Schemes 12 Message Authentication Using Hash Functions: the HMAC Construction 16 Announcements and other data to provide evidence of correct re- covery and to thwart certain attacks. Masked block — a block that results when the for- matted block is masked to hide patterns. Encrypted block — the block that results after the formatted or masked block has been asymmetrically encrypted. For readers interested in some of the security issues involved in using RSA, an earlier CryptoBytes ar- ticle entitled The Secure Use of RSA [9] contains much useful information. PKCS #1 The Public Key Cryptography Standard #1 was de- signed by the cryptographers at RSA Data Secu- rity, Inc. [10]. PKCS #1 describes a method to RSA encrypt a secret symmetric key. The format- ted block is passed directly to the RSA encrypt process. It uses the following method (with ratio- nale): 1. A leading 0x00 is in the block to be RSA en- crypted, ensuring the encryption block is less than the RSA modulus. 2. A block type encoded octet of 0x02 follows the leading 0x00, indicating the block is to be en- crypted using a public key. 3. At least eight non-zero pseudorandom padding octets (bytes) are appended to the right after the block type octet. The padding octets should be generated independently for each RSA en- cryption, especially if the same key is being en- crypted. This thwarts Hastad’s attack [6] and allows use of a low value (e.g., 3) for the public Don B. Johnson and Stephen M. Matyas IBM Cryptography Center of Competence, MS P330 522 South Road Poughkeepsie, NY 12601 USA When public key cryptography was invented, one of its uses was identified as the secure transport of secret symmetric keys. The objectives of such a key transport mechanism keep evolving as attacks are identified, hidden assumptions are revealed, proofs of security are given, and additional capability is needed. The process continues in this article. W e trace the evolution of some asymmetric key transport mechanisms, starting with the method in PKCS #1 [10]. We then discuss, in historical order, two masking techniques developed by IBM cryp- tographers, and the method currently under study in ANSI draft standard X9.44 RSA Key Transport. W e then give ideas that may be useful when using elliptic curve cryptography, where the size of the block is typically much less than that used with other algorithms, for example, RSA. We will use the following terminology: Formatted block — a block of data passed as input to the methods. It contains a secret symmetric key Asymmetric Encryption: Evolution and Enhancements (continued on page 3) Don Johnson, a senior programmer at IBM, is an architect of
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This note was uploaded on 02/05/2011 for the course CS 2105 taught by Professor Ana during the Fall '09 term at National University of Singapore.

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symmetric-enc - Contents 1 Asymmetric E c y t o :E o u i n...

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