According to this post: elliptic curves Adobe Reader only supports specific curves in elliptic cryptography and therefore brainpoolP256r1 is not supported. When I sign the document using brainpool curve I get verification error:
Error during signature verification.
Error encountered while validating:
Internal cryptographic library error.
Error Code: 0x2711
Will these curves be supported in the future releases of Adobe Reader?
[Question moved to the Security & Digital Signatures forum. -Mod]
Are you asking about native support? Acrobat and Reader have a signature plugin architecture that allows third party developers to add signature handlers of any kind to the application. There's nothing stopping anyone from adding this to Acrobat and Reader.
This isn't really about adding a signature handler, but about adding new ECC curves to the current handler. Different incarnations of Acrobat/Reader for Windows/Mac can validate curves other than the FIPS standard P256, P384, P521, but those three are the only ones guaranteed to be supported in all versions. This is a limitation of the crypto libraries used in the product. Adding a new signature handler would mean adding the handler plugin to all copies of Acrobat/Reader that might need to validate Brainpool, which is kind of a non-starter for widespread use (e.g. Brazil and Germany want to use Brainpool for government certificates). You need to find an Acrobat Product Manager and convince him/her that Brainpool support would be a good idea. Good luck.