Struct iso7816_tlv::ber::Tag

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pub struct Tag { /* private fields */ }

Expand description

Tag for BER-TLV data as defined in [ISO7816-4].

Tags can be generated using the TryFrom trait from integer types (see Trait Implementations for valid input types) or hex str.

Tags are now imported in a more permissivie way. Invalid tags in ISO7816 meaning can be checked, see Self::iso7816_compliant

§Example

use std::convert::TryFrom;
use iso7816_tlv::ber::Tag;

assert!(Tag::try_from("80").is_ok());
assert!(Tag::try_from(8u8).is_ok());
assert!(Tag::try_from(8u16).is_ok());
assert!(Tag::try_from(8u32).is_ok());
assert!(Tag::try_from(8i32).is_ok());
assert!(Tag::try_from("7f22").is_ok());

assert!(Tag::try_from("error ").is_err());
assert!(Tag::try_from("7fffff01").is_err());
assert!(Tag::try_from("7f80ff").is_err());
// now more permissive interface :
assert!(Tag::try_from("7f00").is_ok());
assert!(Tag::try_from("7f1e").is_ok());

Implementations§

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impl Tag

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pub fn to_bytes(&self) -> &[u8] ⓘ

serializes the tag as byte array

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pub fn len_as_bytes(&self) -> usize

length of the tag as byte array

§Example

use std::convert::TryFrom;
use iso7816_tlv::ber::Tag;

let tag = Tag::try_from("80")?;
assert_eq!(1, tag.len_as_bytes());

let tag = Tag::try_from("7f22")?;
assert_eq!(2, tag.len_as_bytes());  

let tag = Tag::try_from("7f8122")?;
assert_eq!(3, tag.len_as_bytes());

let tag = Tag::try_from("5fff22")?;
assert_eq!(3, tag.len_as_bytes());

let tag = Tag::try_from("5f2d")?;
assert_eq!(2, tag.len_as_bytes());

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pub fn is_constructed(&self) -> bool

Wether the tag is constructed or not

Bit 6 of the first byte of the tag field indicates an encoding.

The value 0 indicates a primitive encoding of the data object, i.e., the value field is not encoded in BER - TLV .

The value 1 indicates a constructed encoding of the data object, i.e., the value field is encoded in BER - TLV

§Example

use std::convert::TryFrom;
use iso7816_tlv::ber::Tag;

let valid = Tag::try_from(0b0010_0000)?;
assert!(valid.is_constructed());

let invalid = Tag::try_from(0b0000_0001)?;
assert!(!invalid.is_constructed());

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pub fn iso7816_compliant(&self) -> bool

Valid tags are defined as follow:

ISO/IEC 7816 supports tag fields of one, two and three bytes; longer tag fields are reserved for future use

In tag fields of two or more bytes, the values ‘00’ to ‘1E’ and ‘80’ are invalid for the second byte.

In two-byte tag fields, the second byte consists of bit 8 set to 0 and bits 7 to 1 encoding a number greater than thirty. The second byte is valued from ‘1F’ to ’7F; the tag number is from 31 to 127.

In three-byte tag fields, the second byte consists of bit 8 set to 1 and bits 7 to 1 not all set to 0; the third byte consists of bit 8 set to 0 and bits 7 to 1 with any value.

§Example

use std::convert::TryFrom;
use iso7816_tlv::ber::Tag;

let t = Tag::try_from("7f00")?;
assert!(!t.iso7816_compliant());
// 9f1e is a valid EMV tag, but not ISO7816-4 compliant
let t = Tag::try_from("9f1e")?;
assert!(!t.iso7816_compliant());

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pub fn class(&self) -> Class

Get the tag class.

§Example

use std::convert::TryFrom;
use iso7816_tlv::ber::{Tag, Class};

let tag = Tag::try_from(0b0010_0000)?;
assert_eq!(Class::Universal, tag.class());
let tag = Tag::try_from(0b1100_0000)?;
assert_eq!(Class::Private, tag.class());