encoding/asn1: Unmarshal accepts negative dates

[dvyukov]

The following program:

package main

import (
    "encoding/asn1"
    "time"
    "fmt"
)

func main() {
    data := []byte("\x18\x0f00000100000000Z")
    var v time.Time
    _, err := asn1.Unmarshal(data, &v)
    if err != nil {
        return
    }
    fmt.Printf("%v\n",v)
    _, err = asn1.Marshal(v)
    if err != nil {
        panic(err)
    }
}

panics with:

-0001-12-31 00:00:00 +0000 UTC
panic: asn1: structure error: cannot represent time as GeneralizedTime

The value is successfully unmarshalled, but can't be marshalled. I am not sure who exactly is wrong here. This happens because of "date normalization" in time package, it converts day 0 to the last day of the previous month. ASN.1 (ISO 8601) does not define "date normalization", if I understand correctly, assuming that dates and times are valid as is.

I think we should not do time/date normalization, because it is asking for troubles security-wise.

[gopherbot]

CL https://golang.org/cl/11094 mentions this issue.