Merge #16821: Fix bug where duplicate PSBT keys are accepted

9743432034586385cfef87df4b377c255ed0cba8 Fix bug where duplicate PSBT keys are accepted (John L. Jegutanis)

Pull request description:

  As per the BIP 174 spec a PSBT key cannot be duplicated,
  however the current code accepts key duplication.
  The PSBT key/value entries can be duplicated when the value
  is `empty()` or `IsNull()` for `CScript` or `CTxOut` respectively
  and if those key/value entries are serialized before the non-empty ones.

  For example, the following PSBT, included in the test vectors,
  contains a duplicate field:

  ```
  // magic
  70736274ff

  // global tx
  //// key
  0100
  //// value
  2a02000000000140420f000000000017a9146e91b72d5593e7d4391e2ff44e91e985c31641f08700000000
  //// separator
  00

  // no inputs

  // outputs
  //// key PSBT_OUT_WITNESSSCRIPT
  0101
  //// value (empty script)
  00
  //// key PSBT_OUT_WITNESSSCRIPT (same as the above)
  0101
  //// value (an OP_RETURN script)
  016a
  //// separator
  00
  ```

ACKs for top commit:
  achow101:
    ACK 9743432034586385cfef87df4b377c255ed0cba8
  instagibbs:
    code review ACK https://github.com/bitcoin/bitcoin/pull/16821/commits/9743432034586385cfef87df4b377c255ed0cba8

Tree-SHA512: 34f4b34c8e6561c6a6ab745cdd319f6687eac6f7cecc735c94035eeca8c5157e17a27f2ae853dbaa6634fcd5a8f4e1c6cc13d1ebd7e563459665d72bb147cc1e

0 files changed, 0 insertions, 0 deletions