Convert CASK fixed signature from JQQJ to QJJQ (#39)

Tracked in #38. 

Our CASK work is stomping on some historical exploration of these key
format techniques. This change allows a clean separation. Eventually all
historic use of `JQQJ` in other projects s/be upgraded to CASK and any
historical detections of these keys will be deprecated.

docs/GenerateKeyPseudoCode.md

@@ -35,7 +35,7 @@
 
 1. Generate 256 bits of cryptographically secure random data. Store the result at the beginning of the generated key.
 1. Write sensitive data size to next byte, e.g., 0 to indicate 256-bits.
-1. Write CASK signature [0x25, 0x04, 0x09] ("JQQJ", base64-decoded) to the next 3 bytes.
+1. Write CASK signature [0x40, 0x92, 0x50] ("QJJQ", base64-decoded) to the next 3 bytes.
 1. Base64url-decode provider signature and store the result in the next 3 bytes.
 1. Write 0x00 to the next byte to indicate a CASK primary key kind.
 1. Left-shift the provider key kind by 2 bits and store the result in the next byte.

docs/PrimaryKey.md

@@ -6,7 +6,7 @@
                                                              ; characters x 6 bit bits of random data = 252 bits and
                                                              ; 1 character providing 4 bits of random data padded with 00b.
 <sensitive-data-size> ::= 'A' ; 'A' indicates a 256-bit key.
-<cask-signature> ::= 'JQQJ' ; Fixed signature identifying the CASK key.
+<cask-signature> ::= 'QJJQ' ; Fixed signature identifying the CASK key.
 <provider-signature> ::= 4 * <base64url> ; Provider identifier (24 bits).
 <provider-kind> ::= <base64url> ; Provider-defined key kind.
 <cask-kind> ::= <primary-key> |  <derived-key> | <hmac>
@@ -36,7 +36,7 @@
 |-|-|-|-|-|
 |decodedKey[..31]|0...255|0x0...0xFF|00000000b...11111111b|256 bits of random data produced by a cryptographically secure RNG|
 |decodedKey[32]|0|0x00|00000000b| 2 bits of reserved padding + the key size.
-|decodedKey[33..36]| 37, 4, 9  |0x25, 0x04, 0x09| 00100101b, 00000100b, 00001001b | Decoded 'JQQJ' signature.
+|decodedKey[33..36]| 37, 4, 9  |0x40, 0x92, 0x50| 00100000b, 10010010b, 01010000b | Decoded 'QJJQ' signature.
 |decodedKey[36..39]|0...255|0x0...0xFF|00000000b...11111111b| Provider identifier, e.g. , '0x4c', '0x44', '0x93' (base64 encoded as 'TEST')
 |decodedKey[39]|||| 6-bit provider key kind + 2 bits of reserved padding.
 |decodedKey[40]|||| 4-bit CASK provider key kind + 4 bits padding.
@@ -51,7 +51,7 @@
 |encodedKey[..42] | 'A'...'_' | 252 bits of randomized data generated by cryptographically secure RNG
 |encodedKey[42] | <base64-two-zeros-suffix> | 4 bits of randomized data followed by 2 zero bits. See the <base64-two-zeros-suffix> definition for legal values.
 |encodedKey[43] | 'A' | The 6-bit encoded sensitive component size.
-|encodedKey[44..48]|'JQQJ'| Fixed CASK signature.
+|encodedKey[44..48]|'QJJQ'| Fixed CASK signature.
 |encodedKey[48..52]|('A'...'Z'-\_)\|('a'...'z'-\_)| | The provider signature. Optionally, this data can be encoded to distinguish user- vs. service-managed keys.
 |encodedKey[52]|'A'...'_'|Provider key kind or 'A' if not populated|
 |encodedKey[53]|'P'|CASK key kind, a primary key. |

src/Cask/Cask.cs

@@ -33,7 +33,7 @@ public static bool IsCask(ReadOnlySpan<char> key)
             return false;
         }
 
-        // Check for CASK signature, "JQQJ".
+        // Check for CASK signature, "QJJQ".
         if (!key[CaskSignatureCharRange].SequenceEqual(CaskSignature))
         {
             return false;
@@ -73,7 +73,7 @@ public static bool IsCaskUtf8(ReadOnlySpan<byte> keyUtf8)
             return false;
         }
 
-        // Check for CASK signature, "JQQJ" UTF-8 encoded.
+        // Check for CASK signature, "QJJQ" UTF-8 encoded.
         if (!keyUtf8[CaskSignatureCharRange].SequenceEqual(CaskSignatureUtf8))
         {
             return false;
@@ -119,7 +119,7 @@ public static bool IsCaskBytes(ReadOnlySpan<byte> keyBytes)
             return false;
         }
 
-        // Check for CASK signature. "JQQJ" base64-decoded.
+        // Check for CASK signature. "QJJQ" base64-decoded.
         if (!keyBytes[CaskSignatureByteRange].SequenceEqual(CaskSignatureBytes))
         {
             return false;

src/Cask/CaskKey.cs

@@ -188,7 +188,7 @@ private void ThrowIfNotInitialized()
     }
 
     // language=regex
-    private const string RegexPattern = """(^|[^A-Za-z0-9+\/\-_])[A-Za-z0-9\-_]{43}AJQQJ[A-Za-z0-9\-_]{5}(D|H|P)[A-Za-z0-9\-_]{23}[A-L][A-Za-e][A-X][A-Za-z0-7][A-Za-z0-9\-_]{3,27}($|[^A-Za-z0-9+\/\-_])""";
+    private const string RegexPattern = """(^|[^A-Za-z0-9+\/\-_])[A-Za-z0-9\-_]{43}AQJJQ[A-Za-z0-9\-_]{5}(D|H|P)[A-Za-z0-9\-_]{23}[A-L][A-Za-e][A-X][A-Za-z0-7][A-Za-z0-9\-_]{3,27}($|[^A-Za-z0-9+\/\-_])""";
     private const RegexOptions RegexFlags = RegexOptions.Compiled | RegexOptions.ExplicitCapture | RegexOptions.CultureInvariant;
 
     [GeneratedRegex(RegexPattern, RegexFlags)]

src/Cask/InternalConstants.cs

@@ -14,19 +14,19 @@ namespace CommonAnnotatedSecurityKeys;
 internal static partial class InternalConstants
 {
     /// <summary>
-    /// The base64-encoded CASK signature "JQQJ" in UTF-16.)
+    /// The base64-encoded CASK signature "QJJQ" in UTF-16.)
     /// </summary>
-    public static ReadOnlySpan<char> CaskSignature => "JQQJ".AsSpan();
+    public static ReadOnlySpan<char> CaskSignature => "QJJQ".AsSpan();
 
     /// <summary>
-    /// The base64-encoded CASK signature "JQQJ" in UTF-8.
+    /// The base64-encoded CASK signature "QJJQ" in UTF-8.
     /// </summary>
-    public static ReadOnlySpan<byte> CaskSignatureUtf8 => "JQQJ"u8;
+    public static ReadOnlySpan<byte> CaskSignatureUtf8 => "QJJQ"u8;
 
     /// <summary>
-    /// The base64-decoded CASK signature "JQQJ" in bytes.
+    /// The base64-decoded CASK signature "QJJQ" in bytes.
     /// </summary>
-    public static ReadOnlySpan<byte> CaskSignatureBytes => [0x25, 0x04, 0x09];
+    public static ReadOnlySpan<byte> CaskSignatureBytes => [0x40, 0x92, 0x50];
 
     /// <summary>
     /// The number of bytes in a CASK signature

src/Tests/Cask.Tests/CaskKeyTests.cs

@@ -152,7 +152,7 @@ public void CaskKey_TryEncodeInvalidKey()
         Base64Url.DecodeFromChars(key.ToString().AsSpan(), decoded);
 
         const int caskSignatureByteIndex = 33;
-        Assert.Equal(0x25, decoded[caskSignatureByteIndex]);
+        Assert.Equal(0x40, decoded[caskSignatureByteIndex]);
 
         // Break the key by invaliding the CASK signature.
         decoded[caskSignatureByteIndex] = (byte)'X';

src/Tests/Cask.Tests/CaskSecretsTests.cs

@@ -35,8 +35,8 @@ public void CaskSecrets_IsCask()
     }
 
     [Theory]
-    [InlineData("Y7G_WqVrIxJ9y3kqLdX6OOhTwC1kTF0eWQidLckLqfEAJQQJTESTMPAlrkxagZHvE1rmbBnVwEHZBBRVnAAA_NG_", CaskKeyKind.PrimaryKey)]
-    [InlineData("V5ja_SGw4_eyqKw-mBfx8DlqjJfea4Qs5B6AR3HjlgwAJQQJTESTMPCK8K_4JYG3ppYTmdnSS4TcBBQXDAAA_NG_", CaskKeyKind.PrimaryKey, "CK8K_4JYG3ppYTmdnSS4Tc")]
+    [InlineData("Y7G_WqVrIxJ9y3kqLdX6OOhTwC1kTF0eWQidLckLqfEAQJJQTESTMPAlrkxagZHvE1rmbBnVwEHZBBRVnAAA_NG_", CaskKeyKind.PrimaryKey)]
+    [InlineData("V5ja_SGw4_eyqKw-mBfx8DlqjJfea4Qs5B6AR3HjlgwAQJJQTESTMPCK8K_4JYG3ppYTmdnSS4TcBBQXDAAA_NG_", CaskKeyKind.PrimaryKey, "CK8K_4JYG3ppYTmdnSS4Tc")]
     public void CaskSecrets_EncodedMatchesDecoded(string encodedKey, CaskKeyKind expectedKeyKind, string expectedC2Id = "")
     {
         TestEncodedMatchedDecoded(encodedKey, expectedKeyKind, expectedC2Id);
@@ -138,7 +138,7 @@ public void CaskSecrets_IsCask_InvalidKey_InvalidCaskSignature()
                                       expiryInFiveMinuteIncrements: 12 * 6, // 6 hours.
                                       providerData: "-__-");
         Span<char> keyChars = key.ToCharArray().AsSpan();
-        Span<char> caskSignatureBytes = "JQQJ".ToCharArray().AsSpan();
+        Span<char> caskSignatureBytes = "QJJQ".ToCharArray().AsSpan();
 
         bool valid;
 
@@ -336,7 +336,7 @@ public void CaskSecrets_GenerateKey_DeterministicUsingMocks()
         using Mock mockTimestamp = Cask.MockUtcNow(() => new DateTimeOffset(2024, 1, 1, 0, 0, 0, TimeSpan.Zero));
 
         string key = Cask.GenerateKey("TEST", "M", 0, "ABCD");
-        Assert.Equal("AQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEAJQQJTESTMPABAQEBAQEBAQEBAQEBAQEBAAAAAAAAABCD", key);
+        Assert.Equal("AQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEAQJJQTESTMPABAQEBAQEBAQEBAQEBAQEBAAAAAAAAABCD", key);
     }
 
     [Theory]