Comprehensive Explanation

base64

Definition

Base64 is a group of binary-to-text encoding schemes used in computer programming to represent binary data—specifically sequences of 8-bit bytes—as sequences of 24 bits that can be represented by four 6-bit Base64 digits. In the KERI ecosystem, Base64 encoding uses the URL-safe variant (RFC-4648) with the character set [A-Z, a-z, 0-9, -, _], explicitly excluding the = pad character that appears in naive Base64 implementations.

Context in KERI/ACDC

Base64 encoding is foundational to CESR (Composable Event Streaming Representation), which provides the dual text-binary encoding infrastructure for KERI. Within CESR:

• Text Domain Operations: Base64 provides human-readable representation of cryptographic primitives including AIDs, SAIDs, signatures, and digests
• 24-bit Alignment: CESR leverages Base64's 6-bit-per-character encoding to achieve composability through 24-bit boundary alignment (the least common multiple of 6 and 8)
• Derivation Codes: Derivation codes are prepended to Base64-encoded cryptographic material to create self-describing, qualified primitives
• Self-Framing: Base64 encoding enables CESR's self-framing property where primitives contain their own type and length information

KERI specifically uses Base64 URL-File safe encoding variants that replace problematic characters (+ becomes -, / becomes _) for web-based transmission and filename compatibility. This ensures KERI prefixes, events, and credentials can be safely transmitted over HTTP, stored in URLs, and embedded in filenames without escaping.