Raw CRC-32 (IEEE 802.3, the same polynomial as zlib / gzip). Returned as an Int because that’s the natural Erlang form (erlang:crc32/1 returns an unsigned 32-bit integer). Callers wanting the AWS wire form should base64-encode the big-endian 4-byte representation; see crc32_be_bytes for the helper that produces the bytes ready for bit_array.base64_encode.

Big-endian 4-byte encoding of a CRC-32 value, ready to feed into bit_array.base64_encode. AWS’s x-amz-checksum-crc32: <base64> header expects exactly four bytes (not the hex form most other CRC libraries print). Pure Gleam — no FFI hop — because Gleam’s BitArray literal syntax handles the bit packing inline.

Raw CRC-32C (Castagnoli polynomial 0x1EDC6F41, the iSCSI / SCTP variant). Returned as an unsigned 32-bit Int. Implemented in pure Erlang (aws_ffi.crc32c) because OTP’s stdlib doesn’t expose this polynomial. Used by AWS multi-algorithm checksum (crc32c variant) — base64 of the BE 4-byte form goes into x-amz-checksum-crc32c.

Raw MD5 digest. Used by the @httpChecksumRequired body-checksum helper in aws/internal/codec/rest — not by SigV4. MD5 is not a security primitive; the wire spec requires it here so the SDK can emit Content-MD5: base64(md5(body)) for traits that demand it.

Raw SHA-1 digest. Used by the AWS multi-algorithm checksum feature (aws.protocols#httpChecksum) when the caller picks sha1 — the SDK sets x-amz-checksum-sha1: base64(sha1(body)) on the request. SHA-1 isn’t a security primitive on AWS’s side either; it’s a payload-integrity check, and we expose it without warnings because the wire spec mandates it.