| crypto/rand | Package rand implements a cryptographically secure random number generator. |
| encoding/hex | Package hex implements hexadecimal encoding and decoding. |
| errors | Package errors implements functions to manipulate errors. |
| 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. |
| os | Package os provides a platform-independent interface to operating system functionality. |