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Implementing attestation verification

This guide walks through implementing verification of VisualSign parser responses. Before trusting any parsed transaction data, your wallet must verify the attestation to confirm it came from a genuine enclave running the expected code. For background on why verification matters and how the security model works, see Security Model.

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Prerequisites

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Verification levels

Choose the level of verification appropriate for your security requirements:
LevelVerifiesUse Case
Level 1Signature onlyDevelopment and testing
Level 2Signature + PCRsProduction deployments
Level 3Signature + PCRs + ManifestHigh-security environments

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Level 1: Signature verification

Verify the parser’s P256 signature on the response. 
// Extract from parser response
signature := response.ParsedTransaction.Signature
publicKey := signature.PublicKey
message := signature.Message
sig := signature.Signature

// Verify P256 ECDSA signature
valid := verifyP256Signature(publicKey, message, sig)
if !valid {
    return errors.New("invalid signature")
}

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Level 2: Boot attestation

Verify the enclave boot measurements (PCRs) to confirm the expected code is running. 
// Parse attestation document
doc, err := parseAttestationDocument(attestationBytes)
if err != nil {
    return err
}

// Check PCR values against allowlist
expectedPCRs := map[int]string{
    0: "abc123...", // Enclave image
    1: "def456...", // Enclave boot
    2: "ghi789...", // Application hash
}

for idx, expected := range expectedPCRs {
    if doc.PCRs[idx] != expected {
        return fmt.Errorf("PCR%d mismatch", idx)
    }
}

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Level 3: Manifest verification

Verify the exact application binary for complete supply chain verification. 
// Get manifest from attestation
manifest := doc.UserData.Manifest

// Verify manifest signature
manifestSig := manifest.Signature
valid := verifyManifestSignature(manifestSig)

// Check application hash
appHash := sha256.Sum256(applicationBinary)
if manifest.AppHash != appHash {
    return errors.New("application hash mismatch")
}

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Step-by-step implementation

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Step 1: Extract attestation

The parser includes attestation in its responses: 
type ParseResponse struct {
    ParsedTransaction Transaction
    Attestation      []byte // CBOR-encoded attestation document
}

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Step 2: Decode CBOR

AWS attestation documents use CBOR encoding: 
import "github.com/fxamacker/cbor/v2"

var doc AttestationDocument
err := cbor.Unmarshal(attestationBytes, &doc)

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Step 3: Verify certificate chain

The attestation includes an X.509 certificate chain signed by AWS: 
// Extract certificates
certs := doc.Certificate
chain := x509.NewCertPool()

// Build chain
for _, certDER := range certs {
    cert, _ := x509.ParseCertificate(certDER)
    chain.AddCert(cert)
}

// Verify against AWS root CA
opts := x509.VerifyOptions{
    Roots: awsNitroRootCA,
    Intermediates: chain,
}

_, err := leafCert.Verify(opts)

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Step 4: Verify PCR values

Check Platform Configuration Registers against your allowlist: 
type PCRs struct {
    PCR0 []byte // Enclave image file
    PCR1 []byte // Linux kernel and boot ramfs
    PCR2 []byte // Application binary
    PCR3 []byte // Parent instance ID
    PCR4 []byte // Parent instance IP
    PCR8 []byte // Enclave certificate
}
Maintain an allowlist of valid PCR values: 
# pcr-allowlist.yaml
production:
  pcr0: "7fb5c55bc2ecbb68ed99a13d7122abfc0666b926a79d5379bc58b9445c84217f"
  pcr1: "235c9e6050abf6b993c915505f3220e2a82b51a4b8b244d5e19e6c7b2d7e8b25"
  pcr2: "0f0e3e8118b61c8c5b21f92e1e2e52e89d09a92c627d7f6cf42c135f5d5c7c82"

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Step 5: Extract public key

Only extract the public key after successful attestation verification: 
// IMPORTANT: Only after successful attestation verification!
if !verifyAttestation(doc) {
    return errors.New("attestation verification failed")
}

// Now safe to use the public key
publicKey := doc.PublicKey

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Complete example

package verify

import (
    "crypto/ecdsa"
    "crypto/sha256"
    "crypto/x509"
    "encoding/hex"
    "fmt"

    "github.com/fxamacker/cbor/v2"
)

func VerifyParserResponse(resp *ParseResponse) error {
    // Step 1: Decode attestation
    var doc AttestationDocument
    if err := cbor.Unmarshal(resp.Attestation, &doc); err != nil {
        return fmt.Errorf("decode attestation: %w", err)
    }

    // Step 2: Verify certificate chain
    if err := verifyCertificateChain(doc.Certificate); err != nil {
        return fmt.Errorf("verify cert chain: %w", err)
    }

    // Step 3: Check PCR values
    if err := verifyPCRs(doc.PCRs); err != nil {
        return fmt.Errorf("verify PCRs: %w", err)
    }

    // Step 4: Verify signature using attested public key
    pubKey, err := parsePublicKey(doc.PublicKey)
    if err != nil {
        return fmt.Errorf("parse public key: %w", err)
    }

    // Step 5: Verify the transaction signature
    hash := sha256.Sum256([]byte(resp.ParsedTransaction.Payload))
    valid := ecdsa.VerifyASN1(pubKey, hash[:], resp.ParsedTransaction.Signature)
    if !valid {
        return fmt.Errorf("invalid transaction signature")
    }

    return nil
}

func verifyPCRs(pcrs map[int][]byte) error {
    // Load allowlist
    allowlist := loadPCRAllowlist()

    // Check each PCR
    for idx, expected := range allowlist {
        actual := hex.EncodeToString(pcrs[idx])
        if actual != expected {
            return fmt.Errorf("PCR%d mismatch: got %s, want %s",
                idx, actual, expected)
        }
    }

    return nil
}

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PCR management

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Updating your allowlist

When the parser is updated, PCR values change. Follow this process:
  1. Subscribe to parser release announcements
  2. Verify new PCR values against published hashes
  3. Add new PCRs to your allowlist
  4. Deploy to production
  5. Remove old PCRs after migration completes

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Supporting multiple versions

During migrations, support multiple PCR sets: 
# pcr-allowlist.yaml
production:
  # Current version
  - pcr0: "7fb5c55bc..."
    pcr1: "235c9e605..."
    pcr2: "0f0e3e811..."
  # Previous version (remove after migration)
  - pcr0: "a1b2c3d4e..."
    pcr1: "f5g6h7i8j..."
    pcr2: "k9l0m1n2o..."

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Monitoring

Track verification metrics in production: 
metrics.Counter("attestation.verification.success")
metrics.Counter("attestation.verification.failure")
metrics.Histogram("attestation.verification.duration")
Log verification attempts for auditing: 
log.Info("attestation_verified",
    "pcr0", hex.EncodeToString(doc.PCRs[0]),
    "pcr2", hex.EncodeToString(doc.PCRs[2]),
    "timestamp", doc.Timestamp,
    "nonce", doc.Nonce,
)

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Troubleshooting

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PCR mismatch

  • Parser was updated and your allowlist needs updating
  • You’re connecting to a different environment (staging vs production)
  • Check the parser releases for current PCR values

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Certificate chain invalid

  • Check for clock skew on your system
  • Verify certificates haven’t expired
  • Ensure network connectivity for CRL checks

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Signature verification failed

  • Confirm the message being verified matches what was signed
  • Check you’re using the correct public key from the attestation
  • Verify the signature format (ASN.1 DER encoding)

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Debug commands

Check current PCR values on the enclave: 
nitro-cli describe-enclave --enclave-id $EID
Verify an attestation document directly: 
nitro-cli verify-attestation --document attestation.cbor

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Resources