DevPapers - article Digital Signaturesin xml

DSIG signatures may contain either the signed XML object contained in the XML object, or detached from the signed object or document. When the signed XML object envelops the signature, the enveloped signature value itself is not included in the signature calculation and validation computation. For this you use the enveloped-signature transform, removing the whole signature element in which it is contained from the digest calculation.

Public key digital signatures that provide nonrepudiation, such as RSA, are computationally intensive operations; therefore, DSIG also allows shared-key authentication that provides authentication but nonrepudiation.
Collision resistant hashing of the signed content is also used to save computational requirements.

Generating DSIG signatures:
1. Identity resources to be signed.
2. Calculating the digest value and composing reference elements for each resource.
3. Composing the signed info element from all references.
4. Computing value of signature method over identity resources to be signed element by applying algorithms like DSA, RSA-SHA1, etc
5. Composing the signature elements with signedInfo, signature value, identity key used to sign, and other optional objects like signature properties.

An XML DSIG may contain multiple reference elements in the same document