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In cryptography, a public key certificate (also known as a digital certificate or identity certificate) is an electronic document used to prove ownership of a public key. The certificate includes information about the key, information about its owner's identity, and the digital signature of an entity that has verified the certificate's contents are correct. If the signature is valid, and the person examining the certificate trusts the signer, then they know they can use that key to communicate with its owner. In a typical public-key infrastructure (PKI) scheme, the signer is a certificate authority (CA), usually a company which charges customers to issue certificates for them. In a web of trust scheme, the signer is either the key's owner (a self-signed certificate) or other users ("endorsements") whom the person examining the certificate might know and trust. Certificates are an important component of Transport Layer Security (TLS, sometimes called by its older name SSL, Secure Sockets Layer), where they prevent an attacker from impersonating a secure website or other server. They are also used in other important applications, such as email encryption and code signing. ==Operating systems== Certificates can be created for Unix-based servers with tools such as OpenSSL's (ca ) command,〔(OpenSSL: Documentation ca(1) )〕 or SuSE's gensslcert. These may be used to issue unmanaged certificates, certification authority (CA) certificates for managing other certificates, and user or computer certificate requests to be signed by the CA, as well as a number of other certificate related functions. Similarly, Windows Server contains a CA as part of Certificate Services for the creation of digital certificates. In Windows Server 2008 and later the CA may be installed as part of Active Directory Certificate Services. The CA is used to manage and centrally issue certificates to users or computers. Microsoft also provides a number of different certificate utilities, such as SelfSSL.exe for creating unmanaged certificates, and Certreq.exe for creating and submitting certificate requests to be signed by the CA, and certutil.exe for a number of other certificate related functions. Mac OS X comes with the Keychain Access program, which is able to perform various certificate-related services. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Public key certificate」の詳細全文を読む スポンサード リンク
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