PK94987: Encoded string calculates the length of an OCTET STRING incorrectly when the OCTET STRING has constraints

APAR status

• Closed as user error.

Error description

• = SEQUENCE {
  myIdentityInfo OCTET STRING (SIZE (1..255))
  }
  
  and a corresponding TTCN-3 template
  template XYZIdentityType xyzIdentity := {
    myIdentityInfo := '01100110'O
   }
  
  Here, though the actual length of the OCTET STRING
  'myIdentityInfo' is 4, the length bits in the corresponding
  encoded string are represented incorrectly.
  
  When the OCTET STRING is defined without constraints or with the
  constraints OCTET STRING (SIZE (0..255)), the length of the
  string is encoded correctly.
  
  
  Additional Information:
  ***************************
  Here are some of the scenarios that the customer has tested at
  his end, along with the resultant encoded strings:
  
  1. The encoded value when myIdentityInfo is OCTET STRING (SIZE
  (1..255)):
  00 01 00 45 00 00 08 00   03 00 06 00 C0 01 10 01 --- Length is
  calculated as 192 (Incorrect)
  10 00 08 00 0C 40 00 88   00 80 56 76 00 06 AA AA
  
  2. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (2..255)):
  00 01 00 45 00 00 08 00   03 00 06 00 80 01 10 01 --- Length is
  calculated as 128 (Incorrect)
  10 00 08 00 0C 40 00 88   00 80 56 76 00 06 AA AA
  
  3. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (3..255)):
  00 01 00 45 00 00 08 00   03 00 06 00 40 01 10 01 --- Length is
  calculated as 64 (Incorrect)
  10 00 08 00 0C 40 00 88   00 80 56 76 00 06 AA AA
  
  4. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (1..254)):
  00 01 00 45 00 00 08 00   03 00 06 00 C0 01 10 01 --- Length is
  calculated as 192 (Incorrect)
  10 00 08 00 0C 40 00 88   00 80 56 76 00 06 AA AA
  
  5. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (0..255)):
  00 01 00 45 00 00 08 00   03 00 06 00 04 01 10 01 --- Length is
  calculated as 4 (Correct)
  10 00 08 00 0C 40 00 88   00 80 56 76 00 06 AA AA
  
  6. The encoded value when declared myIdentityInfo as OCTET
  STRING:
  00 01 00 45 00 00 08 00   03 00 06 00 04 01 10 01 --- Length is
  calculated as 4 (Correct)
  10 00 08 00 0C 40 00 88   00 80 56 76 00 06 AA AA
  
  Thus the cases where the length is encoded correctly are
  unconstrained Octet string and Octet string with constraint 0 to
  255.
  
  
  Support Investigation:
  ***************************
  The above encoded values are observed by the customer when they
  encode their ASN.1 structured type, that has one of the fields
  as a constrained OCTET STRING.
  
  To test this at the support end we created the attached sample
  test suite and got the following results:
  
  1. The encoded value when myIdentityInfo is OCTET STRING (SIZE
  (1..255)):
  03 01 10 01 10
  
  2. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (2..255)):
  02 01 10 01 10
  
  3. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (3..255)):
  01 01 10 01 10
  
  4. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (1..254)):
  03 01 10 01 10
  
  5. The encoded value when declared myIdentityInfo as OCTET
  STRING (SIZE (0..255)):
  04 01 10 01 10
  
  6. The encoded value when declared myIdentityInfo as OCTET
  STRING:
  04 01 10 01 10
  
  
  
  How to Reproduce:
  *************************
  Build and execute the attached test suite and observe the values
  of the encoded string
  

Local fix

• No WA found
  

Problem summary

Problem conclusion

Temporary fix

Comments

• The current Tester's behavior is correct.
  The cause of encoding difference is that when range is less
  then 256, the actual length is being encoded in bit-field,
  that isn't aligned even in ALIGNED variant (X.691 10.5.7.1)!
  When range is 256 or greater, the encoded length is aligned
  in ALIGNED variant.
  So if before the OCTET STRING field in SEQUENCE we have any
  other field that is encoded in bit-field and some bits are
  not occupied before the octet boundary, in case when OCTET
  STRING is constrained and range is less then 256, the actual
  length bits will be added without alignment.
  

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

Applicable component levels