“Privacy-Enhanced Mail”的意思、由来-开放百科全书

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Privacy-Enhanced Mail

释义

Examples
Privacy-enhanced mail
References

Privacy-Enhanced Mail (PEM) is a de facto file format for storing and sending cryptographic keys, certificates, and other data, based on a set of 1993 IETF standards defining "privacy-enhanced mail." While the original standards were never broadly adopted, and were supplanted by PGP and S/MIME, the textual encoding they defined became very popular. The PEM format was eventually formalized by the IETF in RFC 7468.

Many cryptography standards use ASN.1 to define their data structures, and Distinguished Encoding Rules (DER) to serialize those structures.^[1] Because DER produces binary output, it can be challenging to transmit the resulting files through systems, like electronic mail, that only support ASCII. The PEM format solves this problem by encoding the binary data using base64. PEM also defines a one-line header, consisting of "-----BEGIN ", a label, and "-----", and a one-line footer, consisting of "-----END ", a label, and "-----". The label determines the type of message encoded. Common labels include "CERTIFICATE", "CERTIFICATE REQUEST", "PRIVATE KEY" and "X509 CRL".

PEM data is commonly stored in files with a ".pem" suffix, a ".cer" or ".crt" suffix (for certificates), or a ".key" suffix (for public or private keys).^[2] The label inside a PEM file represents the type of the data more accurately than the file suffix, since many different types of data can be saved in a ".pem" file.

A PEM file may contain multiple instances. For instance, an operating system might provide a file containing a list of trusted CA certificates, or a web server might be configured with a "chain" file containing an end-entity certificate plus a list of intermediate certificates.

Examples

A PEM-encoded certificate:

A PEM-encoded certificate signing request:

Privacy-enhanced mail

The PEM format was first developed in the privacy-enhanced mail series of RFCs: RFC 1421, RFC 1422, RFC 1423, and RFC 1424. These standards assumed prior deployment of a hierarchical public key infrastructure (PKI) with a single root. Such a PKI was never deployed, due to operational cost and legal liability concerns.{{citation needed|date=May 2017}} These standards were eventually obsoleted by PGP and S/MIME, competing e-mail encryption standards.{{citation needed|date=May 2017}}

When working with the PEM format you have to make sure that you are not adding unnecessary line terminations in Windows. Instead use the Unix line termination format. ^[3]

References

1. ^{{Cite web|url=https://tools.ietf.org/html/rfc7468#section-1|title=Textual Encodings of PKIX, PKCS, and CMS Structures|last=Sean|first=Leonard,|last2=Simon|first2=Josefsson,|website=tools.ietf.org|language=en|access-date=2017-03-06}}
2. ^{{Cite web|url=https://support.ssl.com/Knowledgebase/Article/View/19/0/der-vs-crt-vs-cer-vs-pem-certificates-and-how-to-convert-them|title=DER vs. CRT vs. CER vs. PEM Certificates and How To Convert Them|website=support.ssl.com|access-date=2017-03-06}}
3. ^[https://www.hyperaffiliates.com/working-with-pem-files/ Working With Pem Files] hyperaffiliates.com. Retrieved 2019-02-07.

1 : Cryptographic protocols

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