------
## 最终结论
```python
import re

def is_allowed_specific_char(s):
    return bool(re.fullmatch(r'[a-zA-Z0-9]*', s))

# Test cases
assert is_allowed_specific_char("ABCDEFabcdef123450") == True
assert is_allowed_specific_char("*&%@#!}{") == False
assert is_allowed_specific_char("HELLOhowareyou98765") == True
```