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[PersonalData] ​

The [PersonalData] attribute marks a string property as containing personal data that should be encrypted. When EncryptAsync is called, the field's plaintext value is replaced with Base64-encoded AES-256-GCM ciphertext. When DecryptAsync is called, the original value is restored -- unless the encryption key has been deleted (crypto-shredded), in which case a replacement value is returned.

Basic Usage ​

Apply [PersonalData] to any string property alongside a [DataSubjectId] on the same class:

cs
public class ContactInfo
{
    [DataSubjectId]
    public Guid UserId { get; set; }

    [PersonalData]
    public string FirstName { get; set; } = "";

    [PersonalData]
    public string LastName { get; set; } = "";

    [PersonalData]
    public string PhoneNumber { get; set; } = "";
}
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All three fields (FirstName, LastName, PhoneNumber) will be encrypted using the key derived from UserId.

Custom Mask Values ​

The MaskValue property specifies what value is returned when the encryption key has been deleted:

cs
public class UserAccount
{
    [DataSubjectId]
    public Guid Id { get; set; }

    [PersonalData(MaskValue = "[deleted user]")]
    public string DisplayName { get; set; } = "";

    [PersonalData(MaskValue = "deleted@example.com")]
    public string Email { get; set; } = "";

    [PersonalData(MaskValue = "000-00-0000")]
    public string TaxId { get; set; } = "";
}
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After crypto-shredding:

  • DisplayName returns "[deleted user]"
  • Email returns "deleted@example.com"
  • TaxId returns "000-00-0000"

If MaskValue is not set, the default mask value for string fields is an empty string ("").

Groups ​

The Group property links a [PersonalData] field to a specific [DataSubjectId]. This enables multi-key scenarios where different fields on the same entity use different encryption keys:

cs
public class PatientRecord
{
    [DataSubjectId(Group = "medical")]
    public Guid PatientId { get; set; }

    [PersonalData(Group = "medical")]
    public string Diagnosis { get; set; } = "";

    [PersonalData(Group = "medical")]
    public string Treatment { get; set; } = "";

    /// <summary>
    /// Not in the "medical" group — uses a separate key.
    /// </summary>
    [DataSubjectId]
    public Guid RecordId { get; set; }

    [PersonalData]
    public string PatientName { get; set; } = "";
}
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In this example:

  • Diagnosis and Treatment are encrypted with the key derived from PatientId (group "medical").
  • PatientName is encrypted with the key derived from RecordId (default group).
  • Shredding the "medical" group key destroys only the medical data. The patient's name remains decryptable.

Properties Reference ​

PropertyTypeDefaultDescription
Groupstring?nullLinks this field to a [DataSubjectId] with the same group name. Fields without a group use the default (ungrouped) data subject ID.
MaskValuestring?nullValue returned after crypto-shredding. Defaults to "" for strings if not specified.
Maskingstring?nullPartial masking strategy. When set (using a MaskingStrategies constant), a masked version of the value is embedded at encrypt time and returned after shredding instead of MaskValue.
MaskingParameterint0Mode-specific parameter. For MaskAfter, the number of leading characters to preserve. For MaskBefore, the number of trailing characters.

Masking Strategies ​

MaskingStrategies ConstantEffectExample InputExample Output
(not set / null)No masking; uses MaskValue----
MaskAfterKeep first N characters, mask the rest"Jane Doe" (N=2)"Ja******"
MaskBeforeKeep last N characters, mask the rest"Jane Doe" (N=3)"*****Doe"
MaskEmailDomainKeep local part, mask domain"jane@example.com""jane@***.***"

Masking vs. MaskValue

When Masking is set to a MaskingStrategies constant, the masked value is embedded in the ciphertext at encryption time. After crypto-shredding, the masked value is returned instead of the MaskValue string. This allows you to retain partial information (e.g., masked email) while still being GDPR-compliant.

Supported Types ​

[PersonalData] is designed for string properties. For non-string types (int, DateTime, decimal, etc.), use [SerializedPersonalData] instead.

Tayra also supports string collections (List<string>, string[], IList<string>, IReadOnlyList<string>, ICollection<string>). Simply apply [PersonalData] to the collection property and each element will be individually encrypted.

See Also ​