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+.. _signature:
+
+Signature
+---------
+
+.. code-block:: none
+
+    Signature ::= SIGNATURE-TYPE TLV-LENGTH
+                    ( DigestSha256 |
+                      SignatureSha256WithRsa |
+                      SignatureSha256WithRsaAndMerkle |
+                      ... 
+                    )
+
+Signature TLV is a general container of signature, which contains an inner signature TLV. 
+The type field of the inner signature TLV indicates the signing method of the signature, for example,
+
+- ``DigestSha256`` indicates that the integrity of Data is protected by a SHA-256 digest in ``DigestSha256``;
+
+- ``SignatureSha256WithRsa`` indicates that the integrity and provenacne of Data is protected by a RSA signature over a SHA-256 digest;
+
+- ``SignatureSha256WithRsaAndMerkle`` indicates that the integrity and provenance of Data is protected by a RSA signature over SHA-256-Merkle-Hash digest.
+
+If some other types of signatures are required, a new inner signature TLV will be defined.
+
+
+For each inner signature TLV, the last embedded TLV must be a SignatureBits TLV, for example:
+
+.. code-block:: none
+
+    DigestSha256 ::= DIGEST-SHA256-TYPE TLV-LENGTH(=32) SignatureBits(=BYTE[32])
+    
+    SignatureSha256WithRsa ::= SIGNATURE-SHA256-WITH-RSA-TYPE TLV-LENGTH
+                                 KeyLocator
+                                 SignatureBits(=BYTE[32])
+    
+    SignatureSha256WithRsaAndMerkle ::= SIGNATURE-SHA256-WITH-RSA-AND-MERKLE-TYPE 
+                                        TLV-LENGTH
+                                          KeyLocator
+                                          Witness
+                                          SignatureBits(=BYTE[32])
+
+Which fields are covered by the ``SignatureBits`` TLV is up to the signing mechanism.
+A valid signing mechanism, however, must cover following TLVs: Name, MetaInfo (if present), and Content.
+Some signing mechansims may also require the SignatureBits TLV to cover more TLVs.
+For example, ``SignatureSha256WithRsa`` requires the KeyLocator TLV to be signed, 
+and ``SignatureSha256WithRsaAndMerkle`` requires both KeyLocator TLV and Witness TLV to be signed.
+
+For inner signature TLVs that use public key cryptography, the first embedded TLV must be a KeyLocator TLV, e.g., as shown in ``SignatureSha256WithRsa`` and ``SignatureSha256WithRsaAndMerkle`` above.
+
+.. code-block:: none
+
+    KeyLocator ::= KEY-LOCATOR-TYPE TLV-LENGTH CertificateName |
+                   (other types of KeyLocators)
+    CertificateName ::= CERTIFICATE-NAME-TYPE TLV-LENGTH Name
+
+A KeyLocator tells where to find the public key to verify this Data packet. 
+For example, one can specify the name of the certificate of the public key (by CertificateName).
+Name conventions can be used to find the name of the key for a piece of content from the name of the Data packet.
+
+All the other embedded TLVs in an inner signature TLV (such as Witness) are the signature-specific meta information and may vary from a signature type to another.
+
+Changes from CCNx
+~~~~~~~~~~~~~~~~~
+
+- ``Signature`` is moved to the end of Data packet.
+
+- ``KeyLocator`` is moved to be an inner signature block, making the inner signature block self-contained and self-sufficient.
+
+- Signature type (or signing method information) is expressed by the type of inner signature TLV, rather than OID.
+
+- Added support for cheaper signatures
+