Verify a framed authenticated record before using its payload

The capstone is a complete tamper-evident record format and local CLI. A record contains version, context, a Base64 message and a lowercase-hex HMAC tag. The payload remains readable.

The CLI’s sign command computes a shared-key MAC; it is not a public-key digital signature. Every holder of the key can create a valid record. The library verifier releases payload bytes only after accepting the format, caller’s intended context and tag.

Authenticate an unambiguous byte frame, not a casual concatenation. The supplied helper prefixes coderigor.record.v1 plus a zero byte, then a uint64 big-endian context length, context bytes, a uint64 message length and message bytes. The bounds make these allocations small and deliberate.

Version 1 is the only accepted version. The expected context comes from the caller’s operation, not merely from the record itself. An attacker must not move a valid record from one purpose into another.

package main
import ("fmt";"encoding/binary")
func main(){
label,message:="ab",[]byte("c");frame:=binary.BigEndian.AppendUint64(nil,uint64(len(label)));frame=append(frame,[]byte(label)...);frame=binary.BigEndian.AppendUint64(frame,uint64(len(message)));frame=append(frame,message...);fmt.Println(len(frame))
}

The MAC covers decoded semantic fields under the fixed v1 framing. Reordering JSON keys or whitespace can preserve those fields; duplicate JSON keys are rejected by the local adapter to avoid ambiguous parsing. Message and tag encodings must be canonical before authentication.

The download supplies the working reference, starter, standard-library Go module, random-key command, bounded strict JSON adapter, original records, published primitive vectors and tampering tests. It stores a newly generated key in a newly created private file and refuses overwrite. Tests use public fixture keys or an owned temporary directory; no real account secret is needed.

This artifact does not hide payloads or prevent replay. It does not rotate keys, establish human identity or implement a password store. Those require additional protocol/application boundaries. The AEAD lesson supplies the separate maintained encryption operation, while the final CLI remains an integrity-focused artifact.

package main
import ("fmt";"encoding/base64";"bytes")
func main(){
payload:=[]byte{0,255,1};raw:=base64.StdEncoding.EncodeToString(payload);decoded,_:=base64.StdEncoding.DecodeString(raw);fmt.Println(raw,bytes.Equal(payload,decoded))
}

Complete the verifier, download the lab and run its tests and documented keygen/sign/verify sequence in an owned directory. Change the message, tag, context, version or key; verification must fail without outputting accepted payload bytes.

Keep the key private and remove the owned lab key when finished. The visible Boot.dev continuation broadens the cryptographic primitive set; retain these explicit format, context and failure boundaries as you continue.

Download the complete authenticated-record lab: standard-library Go CLI, published vectors, original fixtures, starter, tests and key cleanup instructions.