All standards about ASN.1 (not including standards that use ASN.1 like MMS) are available for free from the ITU under the X.680 to X.697 series of standards.[0]

All standards about ASN.1 (not including standards that use ASN.1 like MMS) are available for free from the ITU under the X.680 to X.697 series of standards.[0] [0]: https://www.itu.int/rec/T-REC-X/en https://www.itu.int/rec/T-REC-X/en