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Audit cryptography as a set of explicit assumptions, not as a search for a single weak hash or signature check. Start by defining the protocol’s assets and trust boundaries, inventory every primitive and key, trace each signed message and hash byte-for-byte, test randomness against the target chain, and verify failure behavior in both contracts and off-chain components. Use the OWASP Smart Contract Security Verification Standard (SCSVS) to choose applicable requirements and the OWASP Smart Contract Security Testing Guide (SCSTG) to turn those requirements into repeatable tests.
What a cryptographic-assumption audit must establish
A useful audit leaves the team able to answer five questions for every cryptographic operation:
- What security property is required: authorization, integrity, collision resistance, secrecy, unpredictability, commitment binding, or something else?
- Which primitive, key, precompile, library, or external service supplies that property?
- What exact bytes, types, domain information, and contract state are covered?
- Which actors can observe, submit, reorder, delay, replace, or influence the operation?
- What happens when input is malformed, duplicated, expired, unverifiable, or produced by a compromised dependency?
The OWASP SCSVS is primarily a requirements baseline for Solidity contracts deployed on EVM-based blockchains. The OWASP SCSTG maps practical tests to SCSVS requirements and to SCWE weaknesses; its page was last updated August 19, 2026. OWASP’s Application Security Verification Standard (ASVS) cryptography chapter is broader application-security guidance. Use its controls as prompts for the whole system, especially off-chain services, but do not present every ASVS control as an EVM-specific rule.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minute| Material | Use during the audit | Scope qualification |
|---|---|---|
| OWASP SCSVS | Select the security requirements that apply to the contract system. | Written primarily for Solidity and EVM-based blockchains. |
| OWASP SCSTG | Choose manual processes, techniques, tools, and test cases that verify selected requirements. | Adapt tests to the actual virtual machine, chain, and architecture. |
| OWASP ASVS 5.0 cryptography controls | Prompt inventory, algorithm, randomness, key-lifecycle, implementation, and failure reviews. | General application guidance; apply it to off-chain and on-chain components where it fits. |
1. Establish scope and the threat model
Freeze the system description before inspecting individual functions. Record the production chain and network, virtual machine behavior, Solidity compiler version, optimizer settings, dependency and library versions, deployed bytecode, verified source correspondence, proxy or upgrade model, and every external contract called by the system. List the assets at risk: tokens, claims, votes, game outcomes, bridge messages, privileged configuration, or user privacy.
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Draw the trust boundaries
Create a diagram that separates contract code from off-chain signers, relayers, front ends, oracle services, bridges, multisignature components, key-custody systems, and external contracts. For each boundary, state what is trusted, what is merely observed, and what can be malicious. A relayer may submit a valid signature without being authorized to create one; an oracle may be honest about a value but unable to provide unpredictable randomness; an external contract may return data that is syntactically valid but economically manipulated.
Describe every signed action
For each authorization, write down the actor that creates the signature, the actor allowed to submit it, the contract that verifies it, and the state transition it authorizes. Include the intended lifetime, nonce or sequence number, target account, target contract, chain or domain identifier, value, function or action name, and any deadline. Mark which state update makes a message one-time and what happens if two submissions race.
Define adversary capabilities
- Can an attacker submit transactions from another account or through another relayer?
- Can block producers, searchers, or users observe signed data before inclusion and influence ordering or timing?
- Can an oracle, bridge validator, signer, upgrade administrator, or external contract be compromised?
- Can an attacker force a callback, return malformed data, consume gas, or make a dependency revert?
- Can the system be upgraded after deployment, and who controls that authority?
These answers determine whether a cryptographic property is actually needed. A signature that is valid forever may still be safe for a one-time migration if state prevents reuse; the same construction is unsafe for a transfer authorization that can be replayed on another chain.
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2. Build a complete cryptographic inventory
Maintain the inventory as a living artifact rather than a design-document appendix. Reconcile it with source code, deployed bytecode, build files, generated clients, signing services, infrastructure configuration, and dependency lockfiles. OWASP ASVS calls for an up-to-date inventory identifying algorithms, keys, certificates, and where keys may be used.
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| Inventory field | What to record |
|---|---|
| Primitive and version | Hash, signature scheme, key-derivation function, encryption or commitment construction, precompile, and exact implementation version. |
| Purpose | Authorization, integrity, collision resistance, second-preimage resistance, commitment, randomness, confidentiality, or another stated property. |
| Input and output encoding | Types, field order, length prefixes, canonicalization, byte order, domain or context fields, output size, and truncation. |
| Key and owner | Public key, signer, custodian, rotation authority, generation method, storage location, and recovery owner. |
| Execution location | Solidity code, EVM precompile, client library, relayer, oracle, bridge service, hardware-backed signer, or other component. |
| Trust assumption | Who must remain honest, what compromise reveals, and what on-chain state limits damage. |
| Failure behavior | Revert, false result, error code, fallback path, retry, partial state update, or accepted default. |
Reconcile documentation with implementation
Search for every hash, signature-recovery call, verification precompile, random-value source, commitment, key derivation, encryption operation, and cryptographic dependency. Include code generated outside the main repository and scripts used to construct calldata. An undocumented helper that packs fields differently from the contract can invalidate an otherwise sound protocol.
Challenge obsolete or custom code
Flag deprecated libraries, copied cryptographic code, hand-written elliptic-curve arithmetic, custom serialization, and algorithms retained only for historical reasons. Determine whether a protocol specification requires the construction. If not, replacing it with an industry-validated implementation is usually safer than preserving compatibility without a documented need. OWASP’s smart-contract guidance specifically warns against deprecated libraries.
3. Audit signatures and authorization end to end
Do not stop at the verifier function. Trace the message from the off-chain signer through serialization, transport, calldata construction, domain separation, recovery or verification, nonce checks, state updates, and event emission.
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- Capture a real signing request and write the fields in order, including their types and widths.
- Reproduce the digest independently from the contract’s implementation and compare every intermediate encoding.
- Check whether dynamic values have unambiguous boundaries and whether canonical forms are enforced.
- Confirm that the signer and verifier use the same domain, version, chain identifier, contract address, and action name where those contexts matter.
- Verify that the displayed human-readable request matches the bytes actually signed; a wallet or service must not show one payload while signing another.
Test replay and cross-context use
- Submit the same signature twice and confirm the second attempt fails without an unintended state change.
- Submit it through a different relayer, account, function, proxy address, or contract instance.
- Try the signature on a fork, another chain, or another deployment where the authorization should not carry over.
- Alter the nonce, deadline, recipient, amount, token, or action field and confirm verification fails.
- Attempt duplicate or out-of-order nonces and inspect whether state remains consistent after failure.
Check forgery and edge cases
Exercise invalid lengths, malformed signatures, zero addresses, zero or maximum values, unsupported signature variants, duplicate signers, and signatures that recover to an unintended account. Confirm that the verifier rejects values outside the supported curve or encoding range and that a failed check cannot be bypassed by a fallback branch. Check whether a signature is accepted after the signer has been removed, rotated, or paused.
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Inspect state ordering
Determine whether nonce consumption and other replay-prevention state are updated before or after external calls. A failed external call, reentrancy path, or out-of-gas condition must not leave a signature reusable when the protocol intended single use. Conversely, a state update must not permanently consume an authorization before the authorized operation has succeeded unless that behavior is explicit.
4. Test randomness assumptions against the target chain
List every outcome that depends on unpredictability: lotteries, games, validator or committee selection, secret generation, randomized allocation, reveal ordering, and challenge selection. For each outcome, identify the entropy source and the parties able to observe or influence it.
Analyze observable and controllable inputs
- Block timestamps, block hashes, transaction ordering, gas prices, and inclusion timing may be observable or influenceable by participants.
- A caller, relayer, oracle, or callback may choose when a request is created or fulfilled.
- Future block data may be unavailable, biased, or changed by chain reorganizations and finality assumptions.
- A commitment-reveal scheme may fail if the reveal deadline, penalty, or non-reveal path lets one party selectively abort.
OWASP identifies secure random generation as an essential cryptographic practice. ASVS 5.0 says non-guessable random values should use a cryptographically secure random number generator (CSPRNG) with at least 128 bits of entropy. That is general application guidance, not a mechanical requirement to call a CSPRNG from a public blockchain. Evaluate the chain-appropriate randomness mechanism, its bias resistance, liveness, cost, and adversary model.
Run bias and prediction tests
- Have an attacker observe all inputs available before commitment, request, or draw time.
- Model the strongest actor who can delay, reorder, censor, or selectively reveal a transaction.
- Check whether changing one controllable input changes the outcome and whether the actor can retry cheaply.
- Test missed callbacks, stale randomness, reorgs, and provider failure.
- Measure the economic value of biasing one outcome against the cost and penalty for attempting it.
5. Review hashes, commitments, and encodings
For each hash, name the required property instead of assuming that a familiar algorithm is sufficient. Collision resistance, second-preimage resistance, integrity, and commitment binding are different claims. A hash can be strong while the protocol’s encoding remains ambiguous.
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Validate the bytes being hashed
- Record exact field order, widths, signedness, length prefixes, padding, and treatment of empty values.
- Check that concatenated variable-length fields cannot produce the same byte string for two logical messages.
- Include contract address, chain or domain context, version, action, and intended recipient when cross-context use would be dangerous.
- Confirm that off-chain and on-chain encoders produce identical bytes for boundary values and Unicode or text inputs.
- Verify whether hashes are truncated, nested, salted, or combined with another digest.
ASVS 5.0 states that when collision resistance is required, a hash output must be at least 256 bits; when only second-preimage resistance is required, the output must be at least 128 bits. Treat those as general cryptographic baselines and verify the protocol’s actual security goal and the chain’s hash semantics. They do not, by themselves, prove that a commitment is binding or that a preimage encoding is unambiguous.
Test commitment lifecycle
Attempt to submit two openings for one commitment, reveal a value under the wrong participant or round, reveal after expiry, and omit a reveal. Check whether the contract distinguishes an invalid opening from a missing one, whether penalties are enforceable, and whether a participant can learn another participant’s secret early through logs, calldata, or an exposed preimage.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.6. Examine implementations, keys, and failure behavior
Prefer validated primitives and safe execution
Identify whether each operation uses a recognized library, platform primitive, or verification precompile. Record exact dependency versions and compiler settings. For off-chain components that handle secrets, review constant-time behavior, secure memory handling, randomness seeding, side-channel exposure, and error paths. A Solidity contract cannot hide data already published on-chain, and no implementation review should imply that public execution provides confidentiality.
Document the key lifecycle
For every private key, document generation, authorization, storage, backup, rotation, revocation, compromise response, and retirement. State who can approve a rotation and how the new public key becomes authoritative on-chain. Include signer quorum rules for multisignature components, emergency pause authority, upgrade keys, oracle credentials, bridge validator keys, and relayer keys. ASVS calls for a documented key-management policy and inventory; adapt that general guidance to the contract’s operational model.
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Verify secure failure
- Malformed signatures, hashes, proofs, and encodings must fail closed rather than select a default signer or value.
- External verification failures must not be converted into a successful authorization.
- Partial state updates must be impossible when a later cryptographic check fails.
- Errors should not leak private keys, secret material, or data that defeats a commitment.
- Retries must be safe and must not create a second authorization, payout, or reveal.
7. Turn requirements into repeatable tests
Use SCSVS requirements to define expected security properties, then select SCSTG test cases and adapt them to the chain and architecture. A test is useful only when another auditor can reproduce it from the record.
| Test record field | Required detail |
|---|---|
| Target | Contract address or component, source and bytecode version, compiler build, and dependency revision. |
| Requirement mapping | Applicable SCSVS requirement and SCWE weakness, when applicable; note any ASVS control used as broader guidance. |
| Preconditions | Accounts, keys, chain state, block conditions, oracle responses, and required permissions. |
| Procedure | Inputs, transaction sequence, signed bytes, fixtures, scripts, and environmental assumptions. |
| Expected result | Precise acceptance or rejection behavior, including state, events, balances, and errors. |
| Observed result | Actual trace, revert, event, recovered signer, digest, or outcome distribution. |
| Limitations | Untested chains, unavailable production keys, provider assumptions, economic scenarios, or properties requiring formal proof. |
Use a layered test set
- Static inventory checks: locate primitives, encoders, key references, randomness sources, and deprecated dependencies.
- Unit tests: verify known signature, hash, encoding, nonce, deadline, and malformed-input vectors.
- Integration tests: exercise signer, relayer, contract, oracle, bridge, and external-call boundaries together.
- Adversarial tests: replay, reorder, duplicate, mutate, delay, censor, reenter, and submit from unauthorized contexts.
- Stateful and economic tests: run sequences across upgrades, rotations, retries, missed reveals, reorg assumptions, and incentive changes.
Report both passing controls and unresolved assumptions. A finding should state the violated property, affected assets, attacker capability, concrete reproduction, severity rationale, and remediation that preserves the intended protocol semantics.
8. Adapt the workflow to non-EVM systems
SCSVS is not a universal checklist for every virtual machine. If the system is not Solidity/EVM-based, retain the workflow—scope, inventory, message tracing, randomness, hashing, key management, testing—but replace EVM-specific requirements with the target platform’s execution, serialization, account, and cryptographic standards. Document which SCSVS or SCSTG items were omitted because they do not map and which platform controls replaced them.
Separate on-chain and off-chain conclusions
State clearly whether a conclusion concerns contract verification, a signer service, a relayer, an oracle, a bridge, or the complete system. An off-chain CSPRNG can generate an unpredictable secret, but publishing that secret or its source on-chain changes the threat model. Likewise, a correct contract verifier cannot compensate for a signer that authorizes the wrong bytes.
Common audit failures and how to correct them
| Failure mode | Correction |
|---|---|
| Checking only the hash algorithm name | Define the required property and inspect exact input encoding, context binding, and output handling. |
| Testing signature validity but not replay | Attempt reuse across calls, relayers, accounts, contracts, chains, and time windows. |
| Assuming block data is random | Model who can observe, delay, reorder, or influence each source and test bias economically. |
| Trusting design documentation | Reconcile documentation with deployed bytecode, generated encoders, scripts, and dependency versions. |
| Applying ASVS literally to public chains | Use ASVS as broad guidance and explain how the platform’s threat model changes the control. |
| Ignoring failure paths | Test malformed input, external reverts, retries, partial updates, and key rotation or compromise. |
| Reporting a tool result without conditions | Record code version, preconditions, expected behavior, observed trace, and limitations for every test. |
Final audit checklist
- Chain, virtual machine, compiler, libraries, deployed bytecode, upgrade model, and assets are documented.
- Trust boundaries include signers, relayers, oracles, bridges, multisignature components, and external contracts.
- Every primitive, key, output, owner, dependency, purpose, and trust assumption appears in the inventory.
- Each signed message has verified field order, types, domain context, nonce, expiry, signer binding, and one-time behavior.
- Malformed, duplicate, expired, forged, and cross-context signatures fail without unintended state changes.
- Every randomness source has a chain-specific unpredictability, bias, liveness, and reorganization analysis.
- Every hash has a stated security property and unambiguous, context-bound encoding.
- Implementations are validated, versions are recorded, and secret-handling components address side channels and failure behavior.
- Key generation, storage, rotation, revocation, backup, compromise response, and multisignature rules are documented.
- Tests map to SCSVS and, where applicable, SCWE and SCSTG, with reproducible procedures and explicit limitations.
The resulting report should make each cryptographic assumption visible, testable, and owned by a specific component or operator. That is the difference between confirming that a contract calls a cryptographic primitive and establishing that the protocol’s security actually depends on properties the implementation and its environment provide.
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