1 files changed, 84 insertions, 0 deletions
diff --git a/crypto/src/asn1/x509/SubjectAltPublicKeyInfo.cs b/crypto/src/asn1/x509/SubjectAltPublicKeyInfo.cs
new file mode 100644
index 000000000..4fe165898
--- /dev/null
+++ b/crypto/src/asn1/x509/SubjectAltPublicKeyInfo.cs
@@ -0,0 +1,84 @@
+using System;
+
+namespace Org.BouncyCastle.Asn1.X509
+{
+    /**
+     * X.509 Section 9.8.2.
+     * <br/>
+     * This public-key certificate extension, when present, shall contain the subject’s alternative public key information
+     * <pre>
+     * subjectAltPublicKeyInfo EXTENSION ::= {
+     *      SYNTAX SubjectAltPublicKeyInfo
+     *      IDENTIFIED BY id-ce-subjectAltPublicKeyInfo }
+     *
+     * SubjectAltPublicKeyInfo ::= SEQUENCE {
+     *     algorithm AlgorithmIdentifier{{SupportedAlgorithms}},
+     *     subjectAltPublicKey BIT STRING }
+     * </pre>
+     * The SubjectAltPublicKeyInfo data type has the following components:
+     * <ul>
+     * <li>the algorithm subcomponent, which shall hold the algorithm that this public key is an instance of</li>
+     * <li>the subjectAltPublicKey subcomponent, which shall hold the alternative public key</li>
+     * </ul>
+     * This extension may be flagged as critical or as non-critical.
+     * <br/>
+     * NOTE – It is recommended that it be flagged as non-critical. Flagging it as critical would require relying parties to understand this
+     * extension and the alternative public-key algorithm.
+     */
+    public class SubjectAltPublicKeyInfo
+        : Asn1Encodable
+    {
+        private readonly AlgorithmIdentifier m_algorithm;
+        private readonly DerBitString m_subjectAltPublicKey;
+
+        public static SubjectAltPublicKeyInfo GetInstance(object obj)
+        {
+            if (obj == null)
+                return null;
+            if (obj is SubjectAltPublicKeyInfo subjectAltPublicKeyInfo)
+                return subjectAltPublicKeyInfo;
+            return new SubjectAltPublicKeyInfo(Asn1Sequence.GetInstance(obj));
+        }
+
+        public static SubjectAltPublicKeyInfo GetInstance(Asn1TaggedObject taggedObject, bool declaredExplicit)
+        {
+            return GetInstance(Asn1Sequence.GetInstance(taggedObject, declaredExplicit));
+        }
+
+        public static SubjectAltPublicKeyInfo FromExtensions(X509Extensions extensions)
+        {
+            return GetInstance(
+                X509Extensions.GetExtensionParsedValue(extensions, X509Extensions.SubjectAltPublicKeyInfo));
+        }
+
+        private SubjectAltPublicKeyInfo(Asn1Sequence seq)
+        {
+            if (seq.Count != 2)
+                throw new ArgumentException("extension should contain only 2 elements");
+
+            m_algorithm = AlgorithmIdentifier.GetInstance(seq[0]);
+            m_subjectAltPublicKey = DerBitString.GetInstance(seq[1]);
+        }
+
+        public SubjectAltPublicKeyInfo(AlgorithmIdentifier algorithm, DerBitString subjectAltPublicKey)
+        {
+            m_algorithm = algorithm;
+            m_subjectAltPublicKey = subjectAltPublicKey;
+        }
+
+        public SubjectAltPublicKeyInfo(SubjectPublicKeyInfo subjectPublicKeyInfo)
+        {
+            m_algorithm = subjectPublicKeyInfo.AlgorithmID;
+            m_subjectAltPublicKey = subjectPublicKeyInfo.PublicKeyData;
+        }
+
+        public AlgorithmIdentifier Algorithm => Algorithm;
+
+        public DerBitString SubjectAltPublicKey => m_subjectAltPublicKey;
+
+        public override Asn1Object ToAsn1Object()
+        {
+            return new DerSequence(m_algorithm, m_subjectAltPublicKey);
+        }
+    }
+}