Subject: PKCS1 update excerpts

From: Jon Callas <[email-masked]>
Date: Tue, 3 Oct 2000 15:15:19 -0700

Please let me know if this is adequate:

5.1:

   The value "m" in the above formulas is derived from the session key
   as follows.  First the session key is prefixed with a one-octet
   algorithm identifier that specifies the symmetric encryption
   algorithm used to encrypt the following Symmetrically Encrypted Data
   Packet.  Then a two-octet checksum is appended which is equal to the
   sum of the preceding session key octets, not including the algorithm
   identifier, modulo 65536.  This value is then encoded as described
   in PKCS-1 block encoding EME-PKCS1-v1_5 [RFC2437] to form the "m"
   value used in the formulas above.

   Note that when an implementation forms several PKESKs with one
   session key, forming a message that can be decrypted by several
   keys, the implementation MUST make new PKCS-1 encoding for each key.

and

5.2.2:

   With RSA signatures, the hash value is encoded as described in
   PKCS-1 section 10.1.2, "Data encoding", producing an ASN.1 value of
   type DigestInfo, and then encoded using PKCS-1 encoding type
   EMSA-PKCS1-v1_5 [RFC2437].  This requires inserting the hash value
   as an octet string into an ASN.1 structure. The object identifier
   for the type of hash being used is included in the structure.  The
   hexadecimal representations for the currently defined hash
   algorithms are:

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From: Erron Criddle <[email-masked]>
Date: Wed, 04 Oct 2000 15:40:27 +0800

Jon,

Does this info help:

The m value is calculated as follows:

boundary        0x00            The boundary value
identifier      0x02            The block type identifier
random  n octets                n octets of non zero PRNG data to make 
len(m) = modulus of the
                                                              length of the 
primary key p
boundary        0x00            The boundary value
algorithm id    1 octet         The ID of the symmetrical algorithm used 
with the session key
session key     n bits          This is the n bit session key to encrypt 
the data
checksum        2 bytes         Is the 16 bit checksum of the session key, 
MOD 65536

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From: Jon Callas <[email-masked]>
Date: Wed, 4 Oct 2000 01:20:56 -0700

I'm trying to clarify and get the references proper. So perhaps, if other
people think it helps.

	Jon