This requirement is from RFC 4880 4.2.2.4. Also simplify the partialLengthWriter loop. The old code worked but was written in a confusing way, with a loop whose terminating condition didn't make sense and was never true in practice. Rewrite it to more clearly do a set of partial writes of decreasing size. Fixes golang/go#32474 Change-Id: Ia53ceb39a34f1d6f2ea7c60190d52948bb0db59b Reviewed-on: https://go-review.googlesource.com/c/crypto/+/181121 Run-TryBot: Ian Lance Taylor <iant@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>