04 hybrid accounts

Hybrid accounts combine both ECDSA and PQC (ML-DSA-65) cryptography, providing defense against both classical and quantum attacks while maintaining full Ethereum compatibility.

Overview

Hybrid accounts are the recommended migration path for users who need quantum resistance without sacrificing compatibility with the existing Ethereum ecosystem.

Technical Specifications

Key Sizes

Component	Size	Format
ECDSA Private Key	32 bytes (256 bits)	Hex string (64 characters)
ECDSA Public Key	64 bytes (512 bits)	Uncompressed (without 0x04)
PQC Private Key	4,032 bytes (32,256 bits)	Hex string (8,064 characters)
PQC Public Key	1,952 bytes (15,616 bits)	Binary/Hex format
Total Private Key	4,064 bytes	Combined storage
Total Public Key	2,016 bytes	Combined storage
Address	20 bytes (160 bits)	Hex format (0x...)
ECDSA Signature	65 bytes	Standard ECDSA
PQC Signature	3,309 bytes	ML-DSA-65
Total Signature	3,374 bytes	Both signatures

Address Derivation

Hybrid accounts use the ECDSA address for backward compatibility:

Hybrid Address = keccak256(ECDSAPublicKey)[12:32]
                = Last 20 bytes of ECDSA public key hash
                = Standard Ethereum address format (0x...)

Alternative (not used):

Hybrid Address = keccak256(ECDSAPublicKey || DilithiumPublicKey)[12:32]

The wallet uses ECDSA address derivation to maintain compatibility with existing Ethereum infrastructure.

Signature Format

Hybrid transactions require both signatures:

Component	Size	Description
ECDSA V	1 byte	Recovery ID
ECDSA R	32 bytes	ECDSA signature component
ECDSA S	32 bytes	ECDSA signature component
PQC Public Key	1,952 bytes	Included in transaction
PQC Signature	3,309 bytes	Dilithium signature
Total Overhead	~5,326 bytes	Per transaction

Both signatures must be valid for the transaction to be accepted.

Address Format

Standard Format (ECDSA-Compatible)

0x742d35Cc6634C0532925a3b844Bc9e7595f8b2a1

• Format: Standard Ethereum address (0x-prefixed hex)

• Length: 40 hex characters (20 bytes)

• Compatibility: Full Ethereum ecosystem compatibility

Bech32m Format (PQC-Enabled)

Hybrid accounts can also be represented in Bech32m format:

pqch1p5cyxnuxmeuwuvkwfem96lqzszee2rssamrj7zc4uy5sw8hgctyq2dlhhw

• HRP: pqch (mainnet) or tpqch (testnet)

• Version: p (version 1, quantum-safe)

• Length: ~62 characters

• Encoding: Bech32m (BIP-350)

When to Use Hybrid Accounts

✅ Use Hybrid When:

• Migration Path Needed

  • Upgrading from ECDSA to quantum-resistant

  • Maintaining existing address compatibility

  • Gradual transition to PQC

• Maximum Security Required

  • Defense against both classical and quantum attacks

  • Critical infrastructure

  • High-value asset storage

• Full Compatibility Needed

  • Must work with existing Ethereum dApps

  • Need standard Ethereum address format

  • Maintaining backward compatibility

• Future-Proofing

  • Preparing for quantum computing era

  • Long-term security planning

  • Regulatory compliance

❌ Don't Use Hybrid When:

• Gas Cost Optimization

  • High-frequency transactions

  • Cost-sensitive operations

  • Hybrid has highest gas costs (~5.3KB overhead)

• PQC-Only Networks

  • Networks that only support PQC (no ECDSA)

  • Pure PQC applications

  • No need for ECDSA compatibility

• Simple Use Cases

  • Temporary accounts

  • Test accounts

  • When quantum threat is not immediate

• Storage Constraints

  • Limited storage for private keys (4KB+)

  • Mobile devices with storage limitations

Security Considerations

Dual Security Model

Hybrid accounts provide defense in depth:

• Classical Security (ECDSA)

  • Protects against current classical attacks

  • Maintains compatibility with existing infrastructure

  • Standard Ethereum security model

• Quantum Security (PQC)

  • Protects against future quantum attacks

  • NIST Level 3 quantum resistance

  • Long-term security guarantee

Security Benefits

• Defense in Depth: Both signatures must be valid

• Attack Resistance: Resistant to both classical and quantum attacks

• Future-Proof: Ready for quantum computing era

• Backward Compatible: Works with existing Ethereum infrastructure

Best Practices

• Secure Key Storage: Both keys must be stored securely (4KB+ total)

• Backup Both Keys: Maintain backups of both ECDSA and PQC keys

• Recovery Phrases: Use mnemonic phrases that can recover both keys

• Network Compatibility: Verify network supports Hybrid transactions

Account Creation

From Random Generation

// Create new Hybrid account
const account = await createHybridAccount(password, keccak256);

From Mnemonic

// Derive Hybrid account from mnemonic
const account = await createHybridAccountFromMnemonic(keccak256);

From Key Import

// Import existing Hybrid account
const ecdsaPrivateKey = "0x1234...";      // 64 hex characters
const ecdsaPublicKey = "0xabcd...";       // 128 hex characters
const dilithiumSecretKey = "0x5678...";   // 8,064 hex characters
const dilithiumPublicKey = "0xef01...";   // 3,904 hex characters

const account = await importHybridAccount(
    ecdsaPrivateKey,
    ecdsaPublicKey,
    dilithiumSecretKey,
    dilithiumPublicKey,
    password,
    keccak256
);

Migration from ECDSA

1

Export ECDSA Private Key

Extract the ECDSA private key from the existing account.

2

Create Hybrid Account

Create a new Hybrid account using the exported ECDSA key and generate the PQC key pair.

3

Transfer Funds

Move funds from the old ECDSA address to the new Hybrid address.

Transaction Signing

Hybrid transactions use HybridTx format (Type 3):

• Transaction Type: Type 3 (HybridTx)

• Signature Format: Both ECDSA and PQC signatures required

• Validation: Both signatures must be valid

• Gas Cost: Highest due to dual signatures (~5.3KB overhead)

Gas Cost Considerations

Hybrid transactions have the highest gas costs:

Component	Size	Approximate Gas Cost
ECDSA Signature	65 bytes	~1,040 gas
PQC Public Key	1,952 bytes	~31,232 gas
PQC Signature	3,309 bytes	~52,944 gas
Total Overhead	~5,326 bytes	~85,216 gas

Gas Cost Comparison:

• ECDSA: ~1,040 gas

• PQC: ~84,176 gas

• Hybrid: ~85,216 gas

Migration Scenarios

Scenario 1: ECDSA to Hybrid

1

Export ECDSA Private Key

Extract from existing account.

2

Create Hybrid Account

Generate PQC key pair, use existing ECDSA key.

3

Transfer Funds

Move funds to new Hybrid address.

4

Update References

Update dApps/contracts to use new address.

Scenario 2: PQC to Hybrid

1

Export PQC Keys

Extract Dilithium key pair.

2

Generate ECDSA Key

Create new ECDSA key pair.

3

Create Hybrid Account

Combine both key pairs.

4

Transfer Funds

Move funds to Hybrid address.

Scenario 3: New Account

1

Create Hybrid Account

Generate both key pairs simultaneously.

2

Fund Account

Send initial funds to Hybrid address.

3

Use Both Signatures

All transactions require both signatures.

Limitations

• Highest Gas Costs: Most expensive transaction type

• Largest Key Storage: Requires storing 4KB+ of private key data

• Dual Signature Requirement: Both signatures must be valid

• Complexity: More complex than single-signature accounts

Advantages

• Maximum Security: Defense against both classical and quantum attacks

• Full Compatibility: Works with existing Ethereum infrastructure

• Future-Proof: Ready for quantum computing era

• Migration Path: Smooth transition from ECDSA to quantum-resistant

Related Documentation

• Account Comparison - Compare all account types

• ECDSA Accounts - Legacy compatible accounts

• PQC Accounts - Quantum-resistant accounts

• When to Use Each Account Type - Decision guide