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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.
Many padding schemes are based on appending predictable data to the final block. For example, the pad could be derived from the total length of the message. This kind of padding scheme is commonly applied to hash algorithms that use the Merkle–Damgård construction such as MD-5, SHA-1, and SHA-2 family such as SHA-224, SHA-256, SHA-384, SHA ...
Mask generation functions were first proposed as part of the specification for padding in the RSA-OAEP algorithm. The OAEP algorithm required a cryptographic hash function that could generate an output equal in size to a "data block" whose length was proportional to arbitrarily sized input message.
The algorithm operates on plaintext blocks of 16 bytes. Encryption of shorter blocks is possible only by padding the source bytes, usually with null bytes. This can be accomplished via several methods, the simplest of which assumes that the final byte of the cipher identifies the number of null bytes of padding added.
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.
RSA (Rivest–Shamir–Adleman) is a public-key cryptosystem, one of the oldest widely used for secure data transmission.The initialism "RSA" comes from the surnames of Ron Rivest, Adi Shamir and Leonard Adleman, who publicly described the algorithm in 1977.
As mentioned in the introduction, the padding scheme used in the Merkle–Damgård construction must be chosen carefully to ensure the security of the scheme. Mihir Bellare gives sufficient conditions for a padding scheme to possess to ensure that the MD construction is secure: it suffices that the scheme be "MD-compliant" (the original length ...