[1] ダイジェストアルゴリズム SHA-256 は、 SHA-256 の RFC 4648 Base64 符号化を表します >>2。

仕様書

[2] RFC 5843 - Additional Hash Algorithms for HTTP Instance Digests (2014-09-14 20:44:32 +09:00 版) http://tools.ietf.org/html/rfc5843#section-2.2
[3] RFC 6249 - Metalink/HTTP: Mirrors and Hashes (2014-09-07 22:47:12 +09:00 版) http://tools.ietf.org/html/rfc6249#section-2

文脈

[4] Metalink/HTTP 鯖は SHA-256 への対応が義務付けられています >>3。

[5] RFC 4055 - Additional Algorithms and Identifiers for RSA Cryptography for use in the Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile (2018-09-02 21:55:48 +09:00) https://tools.ietf.org/html/rfc4055#section-2.1