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Public Key Infrastructure • Chapter 10 577

created by RSA laboratories, the same group that developed the original RSA
encryption standard, along with a consortium of corporations including Microsoft,
Sun, and Apple.The list of active PKCS standards (gaps in the sequence below are
due to standards that have become inactive since they were originally published) is
as follows:

■ PKCS #1: RSA Cryptography Standard Outlines the encryption of data
using the RSA algorithm.The purpose of the RSA Cryptography Standard is
in the development of digital signatures and digital envelopes. PKCS #1 also
describes a syntax for RSA public keys and private keys.The public-key
syntax is used for certificates, while the private-key syntax is used for
encrypting private keys.

■ PKCS #3: Diffie-Hellman Key Agreement Standard Outlines the use
of the Diffie-Hellman Key Agreement, a method of sharing a secret key
between two parties.The secret key is used to encrypt ongoing data transfer
between the two parties.Whitfield Diffie and Martin Hellman developed the
Diffie-Hellman algorithm in the 1970s as the first public asymmetric crypto-
graphic system (asymmetric cryptography was invented in the United
Kingdom earlier in the same decade, but was classified as a military secret).
Diffie-Hellman overcomes the issues of symmetric key systems, because man-
agement of the keys is less difficult.

■ PKCS #5: Password-based Cryptography Standard A method for
encrypting a string with a secret key that is derived from a password.The
result of the method is an octet string (a sequence of 8-bit values). PKCS #8
is primarily used for encrypting private keys when they are being transmitted
between computers.
■ PKCS #6: Extended-certificate Syntax Standard Deals with extended
certificates. Extended certificates are made up of the X.509 certificate plus
additional attributes.The additional attributes and the X.509 certificate can be
verified using a single public-key operation.The issuer that signs the extended
certificate is the same as the one that signs the X.509 certificate.

■ PKCS #7: Cryptographic Message Syntax Standard The foundation
for Secure/Multipurpose Internet Mail Extensions (S/MIME) standard (see
Chapter 3). Is also compatible with Privacy-Enhanced Mail (PEM) and can
be used in several different architectures of key management.
■ PKCS #8: Private-key Information Syntax Standard Describes a
method of communication for private-key information that includes the use

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