Example of AES (Rijndael) CFB encryption in Go. IMHO, http://golang.org/pkg/crypto/cipher/ could benefit a lot from similar snippet.

aes-cfb-example.go

package main

import (
	"crypto/aes"
	"crypto/cipher"
	"fmt"
)

func EncryptAESCFB(dst, src, key, iv []byte) error {
	aesBlockEncrypter, err := aes.NewCipher([]byte(key))
	if err != nil {
		return err
	}
	aesEncrypter := cipher.NewCFBEncrypter(aesBlockEncrypter, iv)
	aesEncrypter.XORKeyStream(dst, src)
	return nil
}

func DecryptAESCFB(dst, src, key, iv []byte) error {
	aesBlockDecrypter, err := aes.NewCipher([]byte(key))
	if err != nil {
		return nil
	}
	aesDecrypter := cipher.NewCFBDecrypter(aesBlockDecrypter, iv)
	aesDecrypter.XORKeyStream(dst, src)
	return nil
}

func main() {
	const key16 = "1234567890123456"
	const key24 = "123456789012345678901234"
	const key32 = "12345678901234567890123456789012"
	var key = key16
	var msg = "message"
	var iv = []byte(key)[:aes.BlockSize] // Using IV same as key is probably bad
	var err error

	// Encrypt
	encrypted := make([]byte, len(msg))
	err = EncryptAESCFB(encrypted, []byte(msg), []byte(key), iv)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Encrypting %v %s -> %v\n", []byte(msg), msg, encrypted)

	// Decrypt	
	decrypted := make([]byte, len(msg))
	err = DecryptAESCFB(decrypted, encrypted, []byte(key), iv)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Decrypting %v -> %v %s\n", encrypted, decrypted, decrypted)
}