This KDF has been defined by the publicly available NIST SP 800-108 specification. NIST SP800-108 allows for alternative orderings of the input fields, meaning that the input can be formated in multiple ways. There are 3 supported formats: - Below [i]_2 is a counter of r-bits length concatenated to the fixedInputData.

• 1: K(i) := PRF( KI, [i]_2 || Label || 0x00 || Context || [L]_2 ) with the counter at the very beginning of the fixedInputData (The default implementation has this format)
• 2: K(i) := PRF( KI, Label || 0x00 || Context || [L]_2 || [i]_2 ) with the counter at the very end of the fixedInputData
• 3a: K(i) := PRF( KI, Label || 0x00 || [i]_2 || Context || [L]_2 ) OR:
• 3b: K(i) := PRF( KI, Label || 0x00 || [i]_2 || [L]_2 || Context ) OR:
• 3c: K(i) := PRF( KI, Label || [i]_2 || 0x00 || Context || [L]_2 ) etc... with the counter somewhere in the 'middle' of the fixedInputData.

This function must be called with the following KDFCounterParameters():

• KI
• The part of the fixedInputData that comes BEFORE the counter OR null
• the part of the fixedInputData that comes AFTER the counter OR null
• the length of the counter in bits (not bytes)

Resulting function calls assuming an 8 bit counter.

• 1. KDFCounterParameters(ki, null, "Label || 0x00 || Context || [L]_2]", 8);
• 2. KDFCounterParameters(ki, "Label || 0x00 || Context || [L]_2]", null, 8);
• 3a. KDFCounterParameters(ki, "Label || 0x00", "Context || [L]_2]", 8);
• 3b. KDFCounterParameters(ki, "Label || 0x00", "[L]_2] || Context", 8);
• 3c. KDFCounterParameters(ki, "Label", "0x00 || Context || [L]_2]", 8);