The value of the SIG_ALGORITHM which specifies the SIG
payload signature algorithm. A GDOI implementation must
support SIG_ALG_RSA.
Following are the Signature Algorithm values defined in
the GDOI RFC 3547, however the CgmGdoiSignatureMethod TC
defines all possible values.
Algorithm Type Value
-------------- -----
RESERVED 0
SIG_ALG_RSA 1
SIG_ALG_DSS 2
SIG_ALG_ECDSS 3
RESERVED 4-127
Private Use 128-255