diff --git a/test/Core.Test/Utilities/EncryptedStringAttributeTests.cs b/test/Core.Test/Utilities/EncryptedStringAttributeTests.cs
new file mode 100644
index 0000000000..f2c8ce816b
--- /dev/null
+++ b/test/Core.Test/Utilities/EncryptedStringAttributeTests.cs
@@ -0,0 +1,43 @@
+using Bit.Core.Utilities;
+using Xunit;
+
+namespace Bit.Core.Test.Utilities
+{
+    public class EncryptedStringAttributeTests
+    {
+        [Theory]
+        [InlineData(null)]
+        [InlineData("aXY=|Y3Q=")] // Valid AesCbc256_B64
+        [InlineData("aXY=|Y3Q=|cnNhQ3Q=")] // Valid AesCbc128_HmacSha256_B64
+        [InlineData("Rsa2048_OaepSha256_B64.cnNhQ3Q=")]
+        public void IsValid_ReturnsTrue_WhenValid(string input)
+        {
+            var sut = new EncryptedStringAttribute();
+
+            var actual = sut.IsValid(input);
+            
+            Assert.True(actual);
+        }
+        
+        [Theory]
+        [InlineData("")]
+        [InlineData(".")]
+        [InlineData("|")]
+        [InlineData("!|!")] // Invalid base 64
+        [InlineData("Rsa2048_OaepSha1_HmacSha256_B64.1")] // Invalid length
+        [InlineData("Rsa2048_OaepSha1_HmacSha256_B64.|")] // Empty iv & ct
+        [InlineData("AesCbc128_HmacSha256_B64.1")] // Invalid length
+        [InlineData("AesCbc128_HmacSha256_B64.aXY=|Y3Q=|")] // Empty mac
+        [InlineData("Rsa2048_OaepSha1_HmacSha256_B64.aXY=|Y3Q=|")] // Empty mac
+        [InlineData("Rsa2048_OaepSha256_B64.1|2")] // Invalid length
+        [InlineData("Rsa2048_OaepSha1_HmacSha256_B64.aXY=|")] // Empty mac
+        public void IsValid_ReturnsFalse_WhenInvalid(string input)
+        {
+            var sut = new EncryptedStringAttribute();
+
+            var actual = sut.IsValid(input);
+            
+            Assert.False(actual);
+        }
+    }
+}