Pushing offset of procedure in asm?

Question

I am trying to acquire a cryption method from an executable file. I have unpacked and started to analyze with IDA Pro.

I have encountered with a code that I couldn't able to understand in any way. Following is asm code block.

___:00A11B6F 008                 mov     eax, [ebp+DecryptedBytes]
___:00A11B72 008                 push    eax
___:00A11B73 00C                 push    100h
___:00A11B78 010                 push    offset CI_StrCmp
___:00A11B7D 014                 mov     ecx, [ebp+LengthValueOfBytes]
___:00A11B80 014                 push    ecx
___:00A11B81 018                 mov     edx, [ebp+Bytes]
___:00A11B84 018                 add     edx, 4
___:00A11B87 018                 push    edx
___:00A11B88 01C                 call    rijndaelDecrypt

And pseudocode of this is:

*(_DWORD *)DecryptResult = rijndaelDecrypt(Bytes + 4, LengthValueOfBytes, (int)CI_StrCmp, 0x100u, DecryptedBytes);

CI_StrCmp is a case insensitive string comparer function. rijndaelDecrypt function reads 16 bytes of this argument. I think it is a key.

Following is rijndaelDecrypt function.

void *__cdecl rijndaelDecrypt(int Bytes, unsigned int Length, int Key, unsigned int BitSize, int a5)
{
  void *DecryptedBytes; // ebx@1
  void *result; // eax@5
  unsigned int v7; // [sp+Ch] [bp-118h]@2
  unsigned int v8; // [sp+10h] [bp-114h]@2
  unsigned int v9; // [sp+14h] [bp-110h]@2
  unsigned int v10; // [sp+18h] [bp-10Ch]@2
  char v11; // [sp+1Ch] [bp-108h]@1

  DecryptedBytes = malloc_2(Length);
  memset(&v11, 0, 0x108u);
  if ( (signed int)BitSize >= 16 )
  {
    v7 = *(_DWORD *)Key;
    v8 = *(_DWORD *)(Key + 4);
    v9 = *(_DWORD *)(Key + 8);
    v10 = *(_DWORD *)(Key + 12);
  }
  else
  {
    v7 = 0x12121212u;
    v8 = 0x12121212u;
    v9 = 0x12121212u;
    v10 = 0x12121212u;
    memcpy(&v7, (const void *)Key, BitSize);
  }
  if ( rijndaelSetupDecrypt((int)&v7, 16, (int)&v11) == 1 )
  {
    sub_A125B0(Bytes, Length, DecryptedBytes, (int)&v11, a5);
    result = DecryptedBytes;
  }
  else
  {
    result = 0;
  }
  return result;
}

My question is what the meaning of sending offset of a procedure to another one is. It makes no sense to me.

p.s. Sorry for my bad English.

Answer 1

Ok I get it... They using the actual code for CL_StrCmp(1) as the key(2) to do the decryption. Code is covered by copyright, so in-order for you decrypt the data in your own program, you must include their code for CL_StrCmp, thus you are infringing on their copyright - IE breaking the law.

(1) The actual compiled instructions for the functions.

(2) Think public\private key.