RFC 3217 (rfc3217) - Page 2 of 9

Triple-DES and RC2 Key Wrapping

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RFC 3217            Triple-DES and RC2 Key Wrapping        December 2001


   In this document, the key words MUST, MUST NOT, REQUIRED, SHOULD,
   SHOULD NOT, RECOMMENDED, and MAY are to be interpreted as described
   by Scott Bradner in [STDWORDS].

2  Key Checksum

   The key checksum algorithm is used to provide a key integrity check
   value.  The algorithm is:

   1. Compute a 20 octet SHA-1 [SHA1] message digest on the key that is
      to be wrapped.
   2. Use the most significant (first) eight octets of the message
      digest value as the checksum value.

3  Triple-DES Key Wrapping and Unwrapping

   This section specifies the algorithms for wrapping and unwrapping one
   Triple-DES key with another Triple-DES key [3DES].

   The same key wrap algorithm is used for both Two-key Triple-DES and
   Three-key Triple-DES keys.  When a Two-key Triple-DES key is to be
   wrapped, a third DES key with the same value as the first DES key is
   created.  Thus, all wrapped Triple-DES keys include three DES keys.
   However, a Two-key Triple-DES key MUST NOT be used to wrap a Three-
   key Triple-DES key that is comprised of three unique DES keys.

3.1  Triple-DES Key Wrap

   The Triple-DES key wrap algorithm encrypts a Triple-DES key with a
   Triple-DES key-encryption key.  The Triple-DES key wrap algorithm is:

   1. Set odd parity for each of the DES key octets comprising the
      Three-Key Triple-DES key that is to be wrapped, call the result
      CEK.
   2. Compute an 8 octet key checksum value on CEK as described above in
      Section 2, call the result ICV.
   3. Let CEKICV = CEK || ICV.
   4. Generate 8 octets at random, call the result IV.
   5. Encrypt CEKICV in CBC mode using the key-encryption key.  Use the
      random value generated in the previous step as the initialization
      vector (IV).  Call the ciphertext TEMP1.
   6. Let TEMP2 = IV || TEMP1.
   7. Reverse the order of the octets in TEMP2.  That is, the most
      significant (first) octet is swapped with the least significant
      (last) octet, and so on.  Call the result TEMP3.
   8. Encrypt TEMP3 in CBC mode using the key-encryption key.  Use an
      initialization vector (IV) of 0x4adda22c79e82105.  The ciphertext
      is 40 octets long.



Housley                      Informational
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