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Base64 標準

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In this guide

This standards reference on Base64Encoding explains standards in plain language for developers and everyday users.

Everything important stays private: try the matching converter or tool in your browser — files and tokens are not uploaded.

Read the full English article below for code samples and edge cases, or switch language anytime from the menu. We keep expanding translations from real user feedback.

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“Base64” is a family of encodings. They all share the same 3-bytes-to-4-characters algorithm but differ in the last two alphabet characters, padding, line wrapping and extra framing.

Standard Chars 62/63 Padding Line length Used in
Standard (RFC 4648 §4) + / required none APIs, JSON, data URIs
MIME (RFC 2045) + / required max. 76 E-mail attachments
PEM (RFC 7468) + / required exactly 64 Certificates, keys
Base64URL (RFC 4648 §5) - _ optional none URLs, JWT, file names
IMAP (RFC 3501) + , none none Mailbox names in modified UTF-7
XML name token / identifier . - / _ : none none XML NMTOKEN and Name values
OpenPGP armor (RFC 4880) + / required max. 76 PGP messages, with CRC-24 checksum

Not sure which one you have? Use the standard detector, then convert between them with normalization.

Standard Base64 The standard Base64 encoding defined in RFC 4648 section 4: alphabet, mandatory padding, no line breaks, canonical encoding and validation regex. Base64URL What Base64URL is, how it differs from standard Base64 (- and _ instead of + and /, no padding), where it is used (JWT, URLs) and how to convert between them. MIME Base64 Base64 Content-Transfer-Encoding for e-mail as defined in RFC 2045: 76-character lines, CRLF line endings, ignored characters and how attachments are encoded. PEM What the PEM format is: Base64-encoded DER data between -----BEGIN----- and -----END----- lines, 64-character line wrapping, common labels and conversion. IMAP How IMAP mailbox names use a Base64 variant with + and , (RFC 3501 modified UTF-7). Alphabet, no padding, and how to decode IMAP Base64 online. XML XML Base64 variants for NMTOKEN (. -) and Name (_ :) values. How they differ from RFC 4648 and when to use them in XML documents. OpenPGP OpenPGP ASCII armor wraps Base64 in BEGIN/END headers with a CRC-24 checksum. How it differs from MIME Base64 and how to decode armored messages online.

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