def METHOD_NAME(self, key_block):
    if key_block < 0 or key_block > 5:
        raise FatalError("Valid key block numbers must be in range 0-5")
    reg, shift = [
        (self.EFUSE_PURPOSE_KEY0_REG, self.EFUSE_PURPOSE_KEY0_SHIFT),
        (self.EFUSE_PURPOSE_KEY1_REG, self.EFUSE_PURPOSE_KEY1_SHIFT),
        (self.EFUSE_PURPOSE_KEY2_REG, self.EFUSE_PURPOSE_KEY2_SHIFT),
        (self.EFUSE_PURPOSE_KEY3_REG, self.EFUSE_PURPOSE_KEY3_SHIFT),
        (self.EFUSE_PURPOSE_KEY4_REG, self.EFUSE_PURPOSE_KEY4_SHIFT),
        (self.EFUSE_PURPOSE_KEY5_REG, self.EFUSE_PURPOSE_KEY5_SHIFT),
    ][key_block]
    return (self.read_reg(reg) >> shift) & 0xF