244 lines
8.3 KiB
Markdown
244 lines
8.3 KiB
Markdown
# StellaOps.Cryptography.Plugin.OfflineVerification
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Cryptographic provider for offline/air-gapped environments using .NET BCL cryptography.
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## Overview
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The `OfflineVerificationCryptoProvider` wraps `System.Security.Cryptography` in the `ICryptoProvider` abstraction, enabling configuration-driven crypto while maintaining offline verification capabilities without external dependencies.
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## Supported Algorithms
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### Signing & Verification
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- **ECDSA**: ES256 (P-256/SHA-256), ES384 (P-384/SHA-384), ES512 (P-521/SHA-512)
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- **RSA PKCS1**: RS256, RS384, RS512
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- **RSA-PSS**: PS256, PS384, PS512
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### Content Hashing
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- **SHA-2**: SHA-256, SHA-384, SHA-512 (supports both `SHA-256` and `SHA256` formats)
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## When to Use
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Use `OfflineVerificationCryptoProvider` when:
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1. **Offline/Air-Gapped Environments**: Systems without network access or external cryptographic services
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2. **Default Cryptography**: Standard NIST-approved algorithms without regional compliance requirements
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3. **Container Scanning**: AirGap module, Scanner module, and other components that need deterministic signing
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4. **Testing**: Local development and testing without hardware security modules
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**Do NOT use when:**
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- Regional compliance required (eIDAS, GOST R 34.10, SM2) - use specialized plugins instead
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- FIPS 140-2 Level 3+ hardware security required - use HSM plugins
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- Key management by external providers - use cloud KMS plugins (AWS KMS, Azure Key Vault, etc.)
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## Usage
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### Basic Hashing
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```csharp
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using StellaOps.Cryptography;
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using StellaOps.Cryptography.Plugin.OfflineVerification;
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var provider = new OfflineVerificationCryptoProvider();
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var hasher = provider.GetHasher("SHA-256");
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var hash = hasher.ComputeHash(data);
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```
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### Signing with Stored Keys
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```csharp
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var provider = new OfflineVerificationCryptoProvider();
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// Add key to provider
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var signingKey = new CryptoSigningKey(
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reference: new CryptoKeyReference("my-key"),
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algorithmId: "ES256",
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privateParameters: ecParameters,
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createdAt: DateTimeOffset.UtcNow);
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provider.UpsertSigningKey(signingKey);
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// Get signer and sign data
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var signer = provider.GetSigner("ES256", new CryptoKeyReference("my-key"));
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var signature = await signer.SignAsync(data);
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```
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### Ephemeral Verification (New in 1.0)
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For scenarios where you only have a public key (e.g., DSSE verification, JWT verification):
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```csharp
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var provider = new OfflineVerificationCryptoProvider();
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// Public key in SubjectPublicKeyInfo (DER-encoded) format
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byte[] publicKeyBytes = ...; // From certificate, JWKS, or inline
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// Create ephemeral verifier
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var verifier = provider.CreateEphemeralVerifier("PS256", publicKeyBytes);
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// Verify signature
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var isValid = await verifier.VerifyAsync(message, signature);
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```
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**Supported Algorithms for Ephemeral Verification:**
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- ECDSA: ES256, ES384, ES512
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- RSA PKCS1: RS256, RS384, RS512
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- RSA-PSS: PS256, PS384, PS512
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**Key Format:**
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- Public keys must be in **SubjectPublicKeyInfo** (SPKI) format (DER-encoded)
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- This is the standard format used in X.509 certificates, JWKs, and TLS
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### Dependency Injection
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```csharp
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services.AddStellaOpsCryptoFromConfiguration(configuration);
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```
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Ensure `etc/crypto-plugins-manifest.json` includes:
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```json
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{
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"id": "offline-verification",
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"name": "OfflineVerificationCryptoProvider",
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"assembly": "StellaOps.Cryptography.Plugin.OfflineVerification.dll",
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"type": "StellaOps.Cryptography.Plugin.OfflineVerification.OfflineVerificationCryptoProvider",
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"capabilities": [
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"signing:ES256", "signing:ES384", "signing:ES512",
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"signing:RS256", "signing:RS384", "signing:RS512",
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"signing:PS256", "signing:PS384", "signing:PS512",
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"hashing:SHA-256", "hashing:SHA-384", "hashing:SHA-512",
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"verification:ES256", "verification:ES384", "verification:ES512",
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"verification:RS256", "verification:RS384", "verification:RS512",
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"verification:PS256", "verification:PS384", "verification:PS512"
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],
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"jurisdiction": "world",
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"compliance": ["NIST", "offline-airgap"],
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"platforms": ["linux", "windows", "osx"],
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"priority": 45,
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"enabledByDefault": true
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}
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```
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## API Reference
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### ICryptoProvider.CreateEphemeralVerifier
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```csharp
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ICryptoSigner CreateEphemeralVerifier(string algorithmId, ReadOnlySpan<byte> publicKeyBytes)
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```
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Creates a verification-only signer from raw public key bytes. Useful for:
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- DSSE envelope verification with inline public keys
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- JWT/JWS verification without key persistence
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- Ad-hoc signature verification in offline scenarios
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**Parameters:**
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- `algorithmId`: Algorithm identifier (ES256, RS256, PS256, etc.)
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- `publicKeyBytes`: Public key in SubjectPublicKeyInfo format (DER-encoded)
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**Returns:**
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- `ICryptoSigner` instance with `VerifyAsync` support only
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- `SignAsync` throws `NotSupportedException`
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- `KeyId` returns `"ephemeral"`
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- `AlgorithmId` returns the specified algorithm
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**Throws:**
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- `NotSupportedException`: If algorithm not supported or public key format invalid
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## Implementation Details
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### Internal Architecture
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```
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OfflineVerificationCryptoProvider (ICryptoProvider)
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├── BclHasher (ICryptoHasher)
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│ └── System.Security.Cryptography.SHA256/384/512
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├── EcdsaSigner (ICryptoSigner)
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│ └── System.Security.Cryptography.ECDsa
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├── RsaSigner (ICryptoSigner)
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│ └── System.Security.Cryptography.RSA
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├── EcdsaEphemeralVerifier (ICryptoSigner)
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│ └── System.Security.Cryptography.ECDsa (verification-only)
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└── RsaEphemeralVerifier (ICryptoSigner)
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└── System.Security.Cryptography.RSA (verification-only)
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```
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### Plugin Boundaries
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**Allowed** within this plugin:
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- Direct usage of `System.Security.Cryptography` (internal implementation)
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- Creation of `ECDsa`, `RSA`, `SHA256`, `SHA384`, `SHA512` instances
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- Key import/export operations
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**Not allowed** outside this plugin:
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- Direct crypto library usage in production code
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- All consumers must use `ICryptoProvider` abstraction
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This boundary is enforced by:
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- `scripts/audit-crypto-usage.ps1` - Static analysis
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- `.gitea/workflows/crypto-compliance.yml` - CI validation
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## Testing
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Run unit tests:
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```bash
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dotnet test src/__Libraries/__Tests/StellaOps.Cryptography.Plugin.OfflineVerification.Tests
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```
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**Test Coverage:**
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- 39 unit tests covering all algorithms and scenarios
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- Provider capability matrix validation
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- Known-answer tests for SHA-256/384/512
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- ECDSA and RSA signing/verification roundtrips
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- Ephemeral verifier creation and usage
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- Error handling (unsupported algorithms, tampered data)
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## Performance
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The abstraction layer is designed to be zero-cost:
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- No heap allocations in hot paths
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- Direct delegation to .NET BCL primitives
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- `ReadOnlySpan<byte>` for memory efficiency
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Benchmark results should match direct `System.Security.Cryptography` usage within measurement error.
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## Security Considerations
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1. **Key Storage**: This provider stores keys in-memory only. For persistent key storage, integrate with a key management system.
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2. **Ephemeral Verification**: Public keys for ephemeral verification are not cached or validated against a trust store. Callers must perform their own trust validation.
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3. **Algorithm Hardening**:
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- RSA key sizes: 2048-bit minimum recommended
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- ECDSA curves: Only NIST P-256/384/521 supported
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- Hash algorithms: SHA-2 family only (SHA-1 explicitly NOT supported)
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4. **Offline Trust**: In offline scenarios, establish trust through:
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- Pre-distributed public key fingerprints
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- Certificate chains embedded in airgap bundles
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- Out-of-band key verification
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## Compliance
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- **NIST FIPS 186-4**: ECDSA with approved curves (P-256, P-384, P-521)
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- **NIST FIPS 180-4**: SHA-256, SHA-384, SHA-512
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- **RFC 8017**: RSA PKCS#1 v2.2 (RSASSA-PKCS1-v1_5 and RSASSA-PSS)
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- **RFC 6979**: Deterministic ECDSA (when used with BouncyCastle fallback)
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**Not compliant with:**
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- eIDAS (European digital signature standards) - use eIDAS plugin
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- GOST R 34.10-2012 (Russian cryptographic standards) - use CryptoPro plugin
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- SM2/SM3/SM4 (Chinese cryptographic standards) - use SM plugin
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## Related Documentation
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- [Crypto Architecture Overview](../../../docs/modules/platform/crypto-architecture.md)
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- [ICryptoProvider Interface](../StellaOps.Cryptography/CryptoProvider.cs)
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- [Plugin Manifest Schema](../../../etc/crypto-plugins-manifest.json)
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- [AirGap Module Architecture](../../../docs/modules/airgap/architecture.md)
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## License
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BUSL-1.1 - See LICENSE file in repository root.
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