Log redaction

Learn how to implement log redaction for sensitive data

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This guide demonstrates how to implement redaction for sensitive information in your OpenTelemetry .NET logs. Redaction is an important practice for protecting sensitive data like personally identifiable information (PII), credentials, and other confidential information.

Why redact logs?

Redacting sensitive information from logs is crucial for:

  1. Compliance: Meeting regulatory requirements like GDPR, HIPAA, or PCI DSS
  2. Security: Preventing exposure of sensitive data in log files or log management systems
  3. Privacy: Protecting user privacy by removing personally identifiable information (PII)
  4. Risk reduction: Minimizing the impact of potential log data breaches

Implementing a basic redaction processor

OpenTelemetry allows you to create custom processors that can modify log records before they’re exported. Here’s how to create a basic redaction processor:

using System.Collections;
using OpenTelemetry;
using OpenTelemetry.Logs;

internal sealed class MyRedactionProcessor : BaseProcessor<LogRecord>
{
    public override void OnEnd(LogRecord logRecord)
    {
        if (logRecord.Attributes != null)
        {
            logRecord.Attributes = new MyClassWithRedactionEnumerator(logRecord.Attributes);
        }
    }

    internal sealed class MyClassWithRedactionEnumerator : IReadOnlyList<KeyValuePair<string, object?>>
    {
        private readonly IReadOnlyList<KeyValuePair<string, object?>> state;

        public MyClassWithRedactionEnumerator(IReadOnlyList<KeyValuePair<string, object?>> state)
        {
            this.state = state;
        }

        public int Count => this.state.Count;

        public KeyValuePair<string, object?> this[int index]
        {
            get
            {
                var item = this.state[index];
                var entryVal = item.Value?.ToString();
                if (entryVal != null && entryVal.Contains("<secret>"))
                {
                    return new KeyValuePair<string, object?>(item.Key, "***REDACTED***");
                }

                return item;
            }
        }

        public IEnumerator<KeyValuePair<string, object?>> GetEnumerator()
        {
            for (var i = 0; i < this.Count; i++)
            {
                yield return this[i];
            }
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return this.GetEnumerator();
        }
    }
}

This processor checks each log attribute value and replaces any that contain the string “” with “REDACTED”.

Using the redaction processor

To use the redaction processor, add it to your OpenTelemetry logging configuration:

using Microsoft.Extensions.Logging;
using OpenTelemetry.Logs;

// Assume MyRedactionProcessor is defined elsewhere
// public class MyRedactionProcessor : BaseProcessor<LogRecord> { ... }

var loggerFactory = LoggerFactory.Create(builder =>
{
    builder.AddOpenTelemetry(logging =>
    {
        logging.AddProcessor(new MyRedactionProcessor());
        logging.AddConsoleExporter();
    });
});

var logger = loggerFactory.CreateLogger<Program>();
// Message will be redacted by MyRedactionProcessor
logger.FoodPriceChanged("", 9.99);

loggerFactory.Dispose();

When you run this code, any log attribute containing “” will be redacted in the output.

Advanced redaction strategies

In real-world applications, you’ll want more sophisticated redaction strategies, either through the SDK or OTel Collector processors.

Here are some approaches that use the SDK:

1. Pattern matching with regular expressions

public KeyValuePair<string, object?> this[int index]
{
    get
    {
        var item = this.state[index];
        var entryVal = item.Value?.ToString();
        if (entryVal != null)
        {
            // Redact credit card numbers
            var redactedValue = Regex.Replace(
                entryVal,
                @"\b(?:\d{4}[-\s]?){3}\d{4}\b",
                "***CARD-REDACTED***");

            // Redact email addresses
            redactedValue = Regex.Replace(
                redactedValue,
                @"\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b",
                "***EMAIL-REDACTED***");

            if (redactedValue != entryVal)
            {
                return new KeyValuePair<string, object?>(item.Key, redactedValue);
            }
        }

        return item;
    }
}

2. Field-based redaction

You may want to redact specific field names regardless of their content:

public KeyValuePair<string, object?> this[int index]
{
    get
    {
        var item = this.state[index];

        // Redact sensitive fields by name
        var sensitiveFields = new[] { "password", "ssn", "creditcard", "api_key" };
        if (sensitiveFields.Any(field => item.Key.Contains(field, StringComparison.OrdinalIgnoreCase)))
        {
            return new KeyValuePair<string, object?>(item.Key, "***REDACTED***");
        }

        return item;
    }
}

3. Partial redaction

For some data types, you might want to show part of the value:

public KeyValuePair<string, object?> this[int index]
{
    get
    {
        var item = this.state[index];
        var entryVal = item.Value?.ToString();

        if (item.Key.Equals("email", StringComparison.OrdinalIgnoreCase) && entryVal != null)
        {
            var parts = entryVal.Split('@');
            if (parts.Length == 2)
            {
                // Show first character of the username and the domain
                var redactedEmail = $"{parts[0][0]}***@{parts[1]}";
                return new KeyValuePair<string, object?>(item.Key, redactedEmail);
            }
        }

        return item;
    }
}

Integration with ASP.NET Core

For ASP.NET Core applications, you can integrate your redaction processor:

builder.Services.AddOpenTelemetry()
    .WithLogging(logging =>
    {
        logging.AddProcessor(new MyRedactionProcessor());
        logging.AddConsoleExporter();
    });

Learn more


Dernière modification August 12, 2025: Add dotnet docs from /docs folder of opentelemetry-dotnet (#7474) (bb927496)