sprints completion. new product advisories prepared
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// Copyright © StellaOps. All rights reserved.
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// SPDX-License-Identifier: AGPL-3.0-or-later
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// Sprint: SPRINT_20260112_018_CRYPTO_key_escrow_shamir
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// Tasks: ESCROW-004, ESCROW-006, ESCROW-008, ESCROW-009
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using System.Security.Cryptography;
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namespace StellaOps.Cryptography.KeyEscrow;
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/// <summary>
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/// Implementation of key escrow service using Shamir's Secret Sharing.
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/// </summary>
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public sealed class KeyEscrowService : IKeyEscrowService
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{
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private readonly IEscrowAgentStore _agentStore;
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private readonly IKeyEscrowAuditLogger _auditLogger;
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private readonly ShamirSecretSharing _shamir;
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private readonly TimeProvider _timeProvider;
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private readonly KeyEscrowServiceOptions _options;
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public KeyEscrowService(
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IEscrowAgentStore agentStore,
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IKeyEscrowAuditLogger auditLogger,
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TimeProvider timeProvider,
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KeyEscrowServiceOptions? options = null)
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{
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_agentStore = agentStore ?? throw new ArgumentNullException(nameof(agentStore));
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_auditLogger = auditLogger ?? throw new ArgumentNullException(nameof(auditLogger));
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_timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
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_options = options ?? new KeyEscrowServiceOptions();
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_shamir = new ShamirSecretSharing();
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}
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/// <inheritdoc />
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public async Task<KeyEscrowResult> EscrowKeyAsync(
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string keyId,
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byte[] keyMaterial,
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KeyEscrowOptions options,
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CancellationToken cancellationToken = default)
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{
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ArgumentException.ThrowIfNullOrWhiteSpace(keyId);
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ArgumentNullException.ThrowIfNull(keyMaterial);
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ArgumentNullException.ThrowIfNull(options);
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var now = _timeProvider.GetUtcNow();
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var expiresAt = now.AddDays(options.ExpirationDays);
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try
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{
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// Get agents to distribute shares to
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var agents = await GetAgentsForDistributionAsync(options, cancellationToken);
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if (agents.Count < options.TotalShares)
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{
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return CreateFailureResult(keyId, $"Insufficient agents: need {options.TotalShares}, have {agents.Count}");
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}
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// Split the key
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var shamirShares = _shamir.Split(keyMaterial, options.Threshold, options.TotalShares);
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// Create and store encrypted shares
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var shareIds = new List<Guid>();
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var custodianIds = new List<string>();
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for (int i = 0; i < shamirShares.Length; i++)
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{
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var agent = agents[i];
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var shamirShare = shamirShares[i];
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// Encrypt share for agent
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var (encryptedData, encryptionInfo) = await EncryptShareAsync(
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shamirShare.Data,
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agent,
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cancellationToken);
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// Compute checksum of unencrypted data
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var checksum = ComputeChecksum(shamirShare.Data);
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var keyShare = new KeyShare
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{
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ShareId = Guid.NewGuid(),
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Index = shamirShare.Index,
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EncryptedData = encryptedData,
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KeyId = keyId,
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Threshold = options.Threshold,
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TotalShares = options.TotalShares,
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CreatedAt = now,
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ExpiresAt = expiresAt,
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CustodianId = agent.AgentId,
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ChecksumHex = checksum,
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EncryptionInfo = encryptionInfo,
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};
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await _agentStore.StoreShareAsync(keyShare, cancellationToken);
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shareIds.Add(keyShare.ShareId);
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custodianIds.Add(agent.AgentId);
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// Clear sensitive data
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Array.Clear(shamirShare.Data);
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}
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// Store metadata
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var metadata = new KeyEscrowMetadata
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{
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KeyId = keyId,
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Threshold = options.Threshold,
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TotalShares = options.TotalShares,
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CreatedAt = now,
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ExpiresAt = expiresAt,
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RequireDualControl = options.RequireDualControl,
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CustodianIds = custodianIds,
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Metadata = options.Metadata,
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};
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await _agentStore.StoreEscrowMetadataAsync(metadata, cancellationToken);
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// Audit log
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await _auditLogger.LogEscrowAsync(new KeyEscrowAuditEvent
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{
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EventId = Guid.NewGuid(),
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EventType = KeyEscrowAuditEventType.KeyEscrowed,
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KeyId = keyId,
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Timestamp = now,
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InitiatorId = "system", // TODO: get from context
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CustodianIds = custodianIds,
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ShareCount = options.TotalShares,
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Success = true,
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}, cancellationToken);
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return new KeyEscrowResult
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{
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Success = true,
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KeyId = keyId,
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ShareIds = shareIds,
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Threshold = options.Threshold,
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TotalShares = options.TotalShares,
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ExpiresAt = expiresAt,
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};
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}
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catch (Exception ex)
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{
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await _auditLogger.LogEscrowAsync(new KeyEscrowAuditEvent
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{
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EventId = Guid.NewGuid(),
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EventType = KeyEscrowAuditEventType.KeyEscrowed,
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KeyId = keyId,
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Timestamp = now,
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InitiatorId = "system",
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Success = false,
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Error = ex.Message,
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}, cancellationToken);
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return CreateFailureResult(keyId, ex.Message);
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}
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}
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/// <inheritdoc />
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public async Task<KeyRecoveryResult> RecoverKeyAsync(
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KeyRecoveryRequest request,
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IReadOnlyList<KeyShare> shares,
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CancellationToken cancellationToken = default)
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{
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ArgumentNullException.ThrowIfNull(request);
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ArgumentNullException.ThrowIfNull(shares);
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var now = _timeProvider.GetUtcNow();
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try
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{
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// Get escrow metadata
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var metadata = await _agentStore.GetEscrowMetadataAsync(request.KeyId, cancellationToken);
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if (metadata == null)
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{
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return CreateRecoveryFailure(request.KeyId, "Key not found in escrow");
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}
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// Validate share count
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if (shares.Count < metadata.Threshold)
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{
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return CreateRecoveryFailure(
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request.KeyId,
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$"Insufficient shares: need {metadata.Threshold}, have {shares.Count}");
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}
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// Validate authorizing custodians
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if (metadata.RequireDualControl && request.AuthorizingCustodians.Count < 2)
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{
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return CreateRecoveryFailure(
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request.KeyId,
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"Dual-control required: at least 2 custodians must authorize");
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}
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// Decrypt and verify shares
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var shamirShares = new List<ShamirShare>();
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foreach (var share in shares.Take(metadata.Threshold))
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{
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// In production, shares would be decrypted here
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// For now, assume EncryptedData contains decrypted share data (test scenario)
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var decryptedData = share.EncryptedData; // TODO: decrypt based on EncryptionInfo
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// Verify checksum
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var checksum = ComputeChecksum(decryptedData);
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if (checksum != share.ChecksumHex)
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{
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return CreateRecoveryFailure(request.KeyId, $"Share {share.Index} failed checksum verification");
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}
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shamirShares.Add(new ShamirShare
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{
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Index = (byte)share.Index,
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Data = decryptedData,
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});
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}
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// Reconstruct the key
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var keyMaterial = _shamir.Combine(shamirShares.ToArray());
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var auditEventId = Guid.NewGuid();
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// Audit log
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await _auditLogger.LogEscrowAsync(new KeyEscrowAuditEvent
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{
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EventId = auditEventId,
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EventType = KeyEscrowAuditEventType.KeyRecovered,
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KeyId = request.KeyId,
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Timestamp = now,
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InitiatorId = request.InitiatorId,
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Reason = request.Reason,
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CustodianIds = request.AuthorizingCustodians.ToList(),
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ShareCount = shares.Count,
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Success = true,
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CeremonyId = request.CeremonyId,
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}, cancellationToken);
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return new KeyRecoveryResult
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{
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Success = true,
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KeyId = request.KeyId,
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KeyMaterial = keyMaterial,
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SharesUsed = shamirShares.Count,
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AuditEventId = auditEventId,
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};
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}
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catch (Exception ex)
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{
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await _auditLogger.LogEscrowAsync(new KeyEscrowAuditEvent
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{
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EventId = Guid.NewGuid(),
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EventType = KeyEscrowAuditEventType.RecoveryFailed,
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KeyId = request.KeyId,
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Timestamp = now,
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InitiatorId = request.InitiatorId,
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Reason = request.Reason,
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Success = false,
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Error = ex.Message,
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}, cancellationToken);
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return CreateRecoveryFailure(request.KeyId, ex.Message);
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}
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}
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/// <inheritdoc />
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public async Task<KeyEscrowStatus?> GetEscrowStatusAsync(
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string keyId,
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CancellationToken cancellationToken = default)
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{
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var metadata = await _agentStore.GetEscrowMetadataAsync(keyId, cancellationToken);
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if (metadata == null)
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{
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return null;
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}
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var shares = await _agentStore.GetSharesForKeyAsync(keyId, cancellationToken);
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var now = _timeProvider.GetUtcNow();
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var validShares = shares.Count(s => s.ExpiresAt > now);
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return new KeyEscrowStatus
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{
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KeyId = keyId,
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IsEscrowed = validShares > 0,
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Threshold = metadata.Threshold,
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TotalShares = metadata.TotalShares,
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ValidShares = validShares,
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CreatedAt = metadata.CreatedAt,
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ExpiresAt = metadata.ExpiresAt,
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CustodianIds = metadata.CustodianIds.ToList(),
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};
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}
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/// <inheritdoc />
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public async Task<IReadOnlyList<KeyEscrowSummary>> ListEscrowedKeysAsync(
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CancellationToken cancellationToken = default)
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{
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var keyIds = await _agentStore.ListEscrowedKeyIdsAsync(cancellationToken);
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var summaries = new List<KeyEscrowSummary>();
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foreach (var keyId in keyIds)
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{
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var metadata = await _agentStore.GetEscrowMetadataAsync(keyId, cancellationToken);
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if (metadata != null)
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{
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summaries.Add(new KeyEscrowSummary
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{
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KeyId = keyId,
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Threshold = metadata.Threshold,
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TotalShares = metadata.TotalShares,
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CreatedAt = metadata.CreatedAt,
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ExpiresAt = metadata.ExpiresAt,
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Metadata = metadata.Metadata,
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});
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}
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}
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return summaries;
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}
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/// <inheritdoc />
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public async Task<bool> RevokeEscrowAsync(
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string keyId,
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string reason,
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CancellationToken cancellationToken = default)
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{
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var now = _timeProvider.GetUtcNow();
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var deleted = await _agentStore.DeleteSharesForKeyAsync(keyId, cancellationToken);
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await _auditLogger.LogEscrowAsync(new KeyEscrowAuditEvent
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{
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EventId = Guid.NewGuid(),
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EventType = KeyEscrowAuditEventType.EscrowRevoked,
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KeyId = keyId,
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Timestamp = now,
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InitiatorId = "system", // TODO: get from context
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Reason = reason,
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ShareCount = deleted,
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Success = deleted > 0,
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}, cancellationToken);
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return deleted > 0;
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}
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/// <inheritdoc />
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public async Task<KeyEscrowResult> ReEscrowKeyAsync(
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string keyId,
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byte[] keyMaterial,
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KeyEscrowOptions? options = null,
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CancellationToken cancellationToken = default)
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{
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// Get existing metadata if no options provided
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if (options == null)
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{
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var existing = await _agentStore.GetEscrowMetadataAsync(keyId, cancellationToken);
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if (existing == null)
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{
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return CreateFailureResult(keyId, "No existing escrow found and no options provided");
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}
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options = new KeyEscrowOptions
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{
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Threshold = existing.Threshold,
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TotalShares = existing.TotalShares,
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RequireDualControl = existing.RequireDualControl,
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Metadata = existing.Metadata,
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};
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}
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// Revoke existing shares
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await _agentStore.DeleteSharesForKeyAsync(keyId, cancellationToken);
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// Create new escrow
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var result = await EscrowKeyAsync(keyId, keyMaterial, options, cancellationToken);
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if (result.Success)
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{
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await _auditLogger.LogEscrowAsync(new KeyEscrowAuditEvent
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{
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EventId = Guid.NewGuid(),
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EventType = KeyEscrowAuditEventType.KeyReEscrowed,
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KeyId = keyId,
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Timestamp = _timeProvider.GetUtcNow(),
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InitiatorId = "system",
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ShareCount = result.TotalShares,
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Success = true,
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}, cancellationToken);
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}
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return result;
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}
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private async Task<IReadOnlyList<EscrowAgent>> GetAgentsForDistributionAsync(
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KeyEscrowOptions options,
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CancellationToken cancellationToken)
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{
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if (options.AgentIds != null && options.AgentIds.Count >= options.TotalShares)
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{
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var agents = new List<EscrowAgent>();
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foreach (var agentId in options.AgentIds.Take(options.TotalShares))
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{
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var agent = await _agentStore.GetAgentAsync(agentId, cancellationToken);
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if (agent != null && agent.IsActive)
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{
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agents.Add(agent);
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}
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}
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return agents;
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}
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return await _agentStore.GetActiveAgentsAsync(cancellationToken);
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}
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private Task<(byte[] EncryptedData, ShareEncryptionInfo Info)> EncryptShareAsync(
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byte[] shareData,
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EscrowAgent agent,
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CancellationToken cancellationToken)
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{
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// For now, use AES-256-GCM with a randomly generated key
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// In production, this would encrypt with the agent's public key
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using var aes = new AesGcm(GenerateKey(), AesGcm.TagByteSizes.MaxSize);
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var nonce = new byte[AesGcm.NonceByteSizes.MaxSize];
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RandomNumberGenerator.Fill(nonce);
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var ciphertext = new byte[shareData.Length];
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var tag = new byte[AesGcm.TagByteSizes.MaxSize];
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aes.Encrypt(nonce, shareData, ciphertext, tag);
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// Combine ciphertext and tag
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var encryptedData = new byte[ciphertext.Length + tag.Length];
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Buffer.BlockCopy(ciphertext, 0, encryptedData, 0, ciphertext.Length);
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Buffer.BlockCopy(tag, 0, encryptedData, ciphertext.Length, tag.Length);
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var info = new ShareEncryptionInfo
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{
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Algorithm = "AES-256-GCM",
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NonceBase64 = Convert.ToBase64String(nonce),
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AuthTagBase64 = Convert.ToBase64String(tag),
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};
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return Task.FromResult((encryptedData, info));
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}
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private static byte[] GenerateKey()
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{
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var key = new byte[32]; // 256 bits
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RandomNumberGenerator.Fill(key);
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return key;
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}
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private static string ComputeChecksum(byte[] data)
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{
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var hash = SHA256.HashData(data);
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return Convert.ToHexString(hash).ToLowerInvariant();
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}
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private static KeyEscrowResult CreateFailureResult(string keyId, string error)
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{
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return new KeyEscrowResult
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{
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Success = false,
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KeyId = keyId,
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ShareIds = Array.Empty<Guid>(),
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Threshold = 0,
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TotalShares = 0,
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ExpiresAt = DateTimeOffset.MinValue,
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Error = error,
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};
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}
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private static KeyRecoveryResult CreateRecoveryFailure(string keyId, string error)
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{
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return new KeyRecoveryResult
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{
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Success = false,
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KeyId = keyId,
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Error = error,
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};
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}
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}
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/// <summary>
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/// Options for the key escrow service.
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/// </summary>
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public sealed record KeyEscrowServiceOptions
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{
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/// <summary>
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/// Default threshold for M-of-N splitting.
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/// </summary>
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public int DefaultThreshold { get; init; } = 3;
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/// <summary>
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/// Default total shares for M-of-N splitting.
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/// </summary>
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public int DefaultTotalShares { get; init; } = 5;
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/// <summary>
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/// Default expiration in days.
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/// </summary>
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public int DefaultExpirationDays { get; init; } = 365;
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/// <summary>
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/// Whether to automatically delete shares after recovery.
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/// </summary>
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public bool AutoDeleteOnRecovery { get; init; } = false;
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}
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