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In cryptography, Optimal Asymmetric Encryption Padding (OAEP) is a padding scheme often used together with RSA encryption. OAEP was introduced by Bellare and Rogaway , [ 1 ] and subsequently standardized in PKCS#1 v2 and RFC 2437.
In cryptography, padding is any of a number of distinct practices which all include adding data to the beginning, middle, or end of a message prior to encryption. In classical cryptography, padding may include adding nonsense phrases to a message to obscure the fact that many messages end in predictable ways, e.g. sincerely yours.
However, the vulnerable padding scheme remains in use and has resulted in subsequent attacks: Bardou et al. (2012) find that several models of PKCS 11 tokens still use the v1.5 padding scheme for RSA. They propose an improved version of Bleichenbacher's attack that requires fewer messages.
PKCS Standards Summary; Version Name Comments PKCS #1: 2.2: RSA Cryptography Standard [1]: See RFC 8017. Defines the mathematical properties and format of RSA public and private keys (ASN.1-encoded in clear-text), and the basic algorithms and encoding/padding schemes for performing RSA encryption, decryption, and producing and verifying signatures.
Standards such as PKCS#1 have been carefully designed to securely pad messages prior to RSA encryption. Because these schemes pad the plaintext m with some number of additional bits, the size of the un-padded message M must be somewhat smaller. RSA padding schemes must be carefully designed so as to prevent sophisticated attacks that may be ...
IFSSA (Integer Factorization Signature Scheme with Appendix): Includes two variants of RSA, Rabin-Williams, and ESIGN, with several message encoding methods. "RSA1 with EMSA3" is essentially PKCS#1 v1.5 RSA signature; "RSA1 with EMSA4 encoding" is essentially RSA-PSS; "RSA1 with EMSA2 encoding" is essentially ANSI X9.31 RSA signature.
Crypto++ ordinarily provides complete cryptographic implementations and often includes less popular, less frequently-used schemes. For example, Camellia is an ISO/NESSIE/IETF-approved block cipher roughly equivalent to AES, and Whirlpool is an ISO/NESSIE/IETF-approved hash function roughly equivalent to SHA; both are included in the library.
Several padding schemes exist. The simplest is to add null bytes to the plaintext to bring its length up to a multiple of the block size, but care must be taken that the original length of the plaintext can be recovered; this is trivial, for example, if the plaintext is a C style string which contains no null bytes except at the end.