| crypto/hmac | Package hmac implements the Keyed-Hash Message Authentication Code (HMAC) as defined in U.S. Federal Information Processing Standards Publication 198. |
| crypto/md5 | Package md5 implements the MD5 hash algorithm as defined in RFC 1321. |
| crypto/tls | Package tls partially implements TLS 1.2, as specified in RFC 5246, and TLS 1.3, as specified in RFC 8446. |
| encoding/base64 | Package base64 implements base64 encoding as specified by RFC 4648. |
| errors | Package errors implements functions to manipulate errors. |
| fmt | Package fmt implements formatted I/O with functions analogous to C's printf and scanf. |
| io | Package io provides basic interfaces to I/O primitives. |
| net | Package net provides a portable interface for network I/O, including TCP/IP, UDP, domain name resolution, and Unix domain sockets. |
| net/textproto | Package textproto implements generic support for text-based request/response protocols in the style of HTTP, NNTP, and SMTP. |
| strings | Package strings implements simple functions to manipulate UTF-8 encoded strings. |