ascii_to_bin(char ch)
{
	if (ch > 'z')
		return (0);
	if (ch >= 'a')
		return (ch - 'a' + 38);
	if (ch > 'Z')
		return (0);
	if (ch >= 'A')
		return (ch - 'A' + 12);
	if (ch > '9')
		return (0);
	if (ch >= '.')
		return (ch - '.');
	return (0);
}

This weakness pertains to the use of cryptographic functions that are weak, misconfigured, or outdated, which undermines the intended protection of encrypted data and communications.