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8.3. Use of Contexts

8.3. Use of Contexts​

Contexts can be used to separate uses of the protocol between different protocols (which is very hard to reliably do otherwise) and between different uses within the same protocol. However, the following SHOULD be kept in mind when using this facility:

  • The context SHOULD be a constant string specified by the protocol using it. It SHOULD NOT incorporate variable elements from the message itself.

  • Contexts SHOULD NOT be used opportunistically, as that kind of use is very error prone. If contexts are used, one SHOULD require all signature schemes available for use in that purpose support contexts.

  • Contexts are an extra input, which percolate out of APIs; as such, even if the signature scheme supports contexts, those may not be available for use. This problem is compounded by the fact that many times the application is not invoking the signing and verification functions directly but via some other protocol.

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