
Unique citizenship number

The uniform civil number (; abbreviated: ЕГН, "EGN") is a 10-digit unique string assigned to each Bulgarian citizen or resident foreign national. It serves as a national identification number. An EGN is assigned to Bulgarians at birth, or when a birth certificate is issued. The "uniform system for civil registration and administrative service of population" (; abbreviated: ЕСГРАОН, "ESGRAON") regulates the EGN system.
Structure.
The initial six digits correspond to the birth date (YYMMDD). Since there are only two digits reserved for the year, only years between 1900 and 1999 can be encoded directly. Other years get represented as follows:
The next three digits designate the birth order number, the third digit being even for males and odd for females. Each district is assigned a range of three-digit numbers, used consecutively, altering even and odd numbers between males and females born on the particular day. In rare cases, numbers are "borrowed" from an adjacent district.
The tenth digit is a checksum, calculated using the following algorithm:
 | Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
 | Weight | x2 | x4 | x8 | x5 | x10 | x9 | x7 | x3 | x6 | |
The weights are the powers of 2, modulo 11. ("See also": Galois field applications)
Misuse.
In order to easily cross borders criminals have been known to change EGNs. There were 46 such cases detected in March 2005.
Using the EGN system for identification raised some privacy concerns, though they are officially considered personal information and are protected by law.