Question on <draft-ietf-smime-msg-00.txt>

Hi All

   I have a question regarding to MUST implement algorithms.
   In <draft-ietf-smime-msg-00.txt> section 2.3 says....

> 2.3 KeyEncryptionAlgorithmIdentifier
>
> Sending and receiving agents MUST support Diffie-Hellman defined in[DH].
>
> Receiving agents SHOULD support rsaEncryption. Incoming encrypted
> messages contain symmetric keys which are to be decrypted with a
> user's private key. The size of the private key is determined during
> key generation.Sending agents SHOULD support rsaEncryption. 
>
> Sending agents MUST support encryption of symmetric keys with RSA
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> public keys at key sizes from 512 bits to 1024 bits.   
 ~~~~~~~~~~~~~

   Is that mean Sending agents MUST support RSA algorithm?
   Sorry if I misunderstood the sentence.
   
                                  Thanks in advance.
   
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  Makoto Tomoeda

  NTT Multimedia Communication Promotion Dept.
  Security Service Project Group
  E-mail : tomoeda(_dot_)makoto(_at_)nsc(_dot_)cae(_dot_)ntt(_dot_)co(_dot_)jp
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