OpenPGP -> cryptographic

gpgsig in revisions not necessarily OpenPGP

Signed-off-by: Castedo Ellerman <castedo@castedo.com>

Chapters/5.Core_identifiers.md

@@ -91,7 +91,7 @@ The supported metadata is as follows:
 - committer timezone offset (arbitrary byte sequence): UTC offset at which the revision was committed, usually an ASCII-encoded [+/-]HHMM specification.
 - directory (mandatory): the root directory recorded by the revision
 - parent revisions (ordered list of revisions): the immediately preceding revisions in the development timeline. Can be empty for an initial revision, and have multiple revisions when multiple branches of history are being merged.
-- extra headers (ordered list of byte key/value pairs): arbitrary additional metadata attached to the revision. The key must not contain the ASCII bytes for the space or LF characters; commonly used keys are a string of non-whitespace printable ASCII characters, such as `"encoding"` (where the value is interpreted as the encoding of the message field) or `"gpgsig"` (where the value is interpreted as an OpenPGP signature of the metadata of the revision).
+- extra headers (ordered list of byte key/value pairs): arbitrary additional metadata attached to the revision. The key must not contain the ASCII bytes for the space or LF characters; commonly used keys are a string of non-whitespace printable ASCII characters, such as `"encoding"` (where the value is interpreted as the encoding of the message field) or `"gpgsig"` (where the value is interpreted as a cryptographic signature of the metadata of the revision).
 - message: the message describing the revision
 
 In order to compute the intrinsic identifier of a revision, it is necessary to first compute the intrinsic identifier of the root directory recorded by the revision, as well as the intrinsic identifier of all parent revisions (recursively).