Message M:
1 |6C 69 63 65 6E 73 65 20 31 39 32 2E 31 36 38 2E
2 |32 33 39 2E 31 32 39 20 31 33 6A 61 6E 32 30 31
3 |37 20 63 70 73 6D 2D 63 2D 75 20 63 70 73 62 2D
4 |6E 70 6D 20 63 70 73 62 2D 65 70 6D 20 63 70 73
5 |62 2D 6C 6F 67 73 20 63 70 73 62 2D 6D 6E 74 72
6 |20 63 70 73 62 2D 70 72 76 73 20 63 70 73 62 2D
7 |75 64 69 72 20 63 70 73 62 2D 77 6B 66 6C 2D 31
8 |30 30 20 63 70 73 62 2D 77 73 20 63 70 73 62 2D
9 |6D 70 74 6C 20 63 70 76 70 2D 73 6E 78 2D 75 2D
10 |6E 67 78 20 63 70 73 62 2D 73 77 62 20 63 70 73
11 |62 2D 61 64 6E 63 2D 6D 20 63 70 73 62 2D 72 70
12 |72 74 2D 75 20 63 70 73 62 2D 65 76 63 72 2D 75
13 |20 63 70 73 62 2D 63 6F 6D 70 2D 75 20 63 70 73
14 |62 2D 73 73 6C 76 70 6E 2D 6D 6F 62 6D 61 69 6C
15 |2B 35 30 30 30 20 63 6B 2D 39 62 31 35 64 65 61
16 |39 30 39 32 64 0A
To verify, we have 2 parameters (Tag1 and A - big number)
Tag1
1 |07 31 5F CE F8 E6 92 03
Tag2 depends on Tag1 as below (c1, c2, c3 is fixed big number)
d = A / 2^61
e = ( c2 ^ d ) mod c3
g = ( c1 ^ Tag1 ) mod c3
Tag2 = ( e x g ) mod c3
Tag2
1 |B5 03 6C A3 1E 03 C4 5F C3 CE E3 F5 3C AE 46 04
2 |EA FD 71 17 5D 69 31 AC D1 37 86 E3 D0 25 A0 1B
3 |EB 9E 1C ED 1B 99 16 0E D3 B3 DD 89 B1 93 3C 24
4 |51 79 FC 7B 41 E2 EC 7B 16 3A 8F 34 CB 95 90 80
5 |15 F6 01 67 85 72 40 2D EC 83 6E 95 6E 5C 37 BF
6 |03 44 15 7D 3D 21 F3 71 CF F6 19 23 2A 31 A3 D7
7 |64 86 13 E6 58 80 71 93 2E DD E5 30 3A 8F 04 99
8 |00 26 C7 E4 04 51 82 07 B0 B2 9B 1D 89 19 D4 9F
9 |00
SHA-1(M||Tag2)
1 |07 31 5F CE F8 E6 92 03 9C 43 28 C6 F0 38 57 43 2 |D3 2C D9 34
Scenario:
I have Message M (bytes) as above. In order to authenticate the
message, I was provided Tag1 and parameter A to verify the message M. From
the result of SHA-1(M||Tag2), we can see that the first 8 bytes are exact
same as Tag1, that means the message M is authenticated.
My questions:
I don't know how tag1 and tag2 were generated but can ensure that they
will be relevant to message M.
Which possible algorithm / model they used to generate Tag1 and
parameter A that can make SHA-1 result as expected (matched Tag1), as I
know SHA-1 is one-way hashing that we can't predict the input that can
genrate expected output.
On Tue, Jan 10, 2017 at 1:28 AM, <[email protected]> wrote:
>
>
> Message M:
>
> 1 |6C 69 63 65 6E 73 65 20 31 39 32 2E 31 36 38 2E
>
> 2 |32 33 39 2E 31 32 39 20 31 33 6A 61 6E 32 30 31
>
> 3 |37 20 63 70 73 6D 2D 63 2D 75 20 63 70 73 62 2D
>
> 4 |6E 70 6D 20 63 70 73 62 2D 65 70 6D 20 63 70 73
>
> 5 |62 2D 6C 6F 67 73 20 63 70 73 62 2D 6D 6E 74 72
>
> 6 |20 63 70 73 62 2D 70 72 76 73 20 63 70 73 62 2D
>
> 7 |75 64 69 72 20 63 70 73 62 2D 77 6B 66 6C 2D 31
>
> 8 |30 30 20 63 70 73 62 2D 77 73 20 63 70 73 62 2D
>
> 9 |6D 70 74 6C 20 63 70 76 70 2D 73 6E 78 2D 75 2D
>
> 10 |6E 67 78 20 63 70 73 62 2D 73 77 62 20 63 70 73
>
> 11 |62 2D 61 64 6E 63 2D 6D 20 63 70 73 62 2D 72 70
>
> 12 |72 74 2D 75 20 63 70 73 62 2D 65 76 63 72 2D 75
>
> 13 |20 63 70 73 62 2D 63 6F 6D 70 2D 75 20 63 70 73
>
> 14 |62 2D 73 73 6C 76 70 6E 2D 6D 6F 62 6D 61 69 6C
>
> 15 |2B 35 30 30 30 20 63 6B 2D 39 62 31 35 64 65 61
>
> 16 |39 30 39 32 64 0A
>
> Tag1
>
> 1 |07 31 5F CE F8 E6 92 03
>
> Tag2
>
> 1 |B5 03 6C A3 1E 03 C4 5F C3 CE E3 F5 3C AE 46 04
>
> 2 |EA FD 71 17 5D 69 31 AC D1 37 86 E3 D0 25 A0 1B
>
> 3 |EB 9E 1C ED 1B 99 16 0E D3 B3 DD 89 B1 93 3C 24
>
> 4 |51 79 FC 7B 41 E2 EC 7B 16 3A 8F 34 CB 95 90 80
>
> 5 |15 F6 01 67 85 72 40 2D EC 83 6E 95 6E 5C 37 BF
>
> 6 |03 44 15 7D 3D 21 F3 71 CF F6 19 23 2A 31 A3 D7
>
> 7 |64 86 13 E6 58 80 71 93 2E DD E5 30 3A 8F 04 99
>
> 8 |00 26 C7 E4 04 51 82 07 B0 B2 9B 1D 89 19 D4 9F
>
> 9 |00
>
> SHA-1(M||Tag2)
>
> 1 |07 31 5F CE F8 E6 92 03 9C 43 28 C6 F0 38 57 43 2 |D3 2C D9 34
>
> Scenario:
>
> I have Message M (bytes) as above. In order to authenticate the
> message, I was provided Tag1 and Tag2. From the result of SHA-1(M||Tag2),
> we can see that the first 8 bytes is exact same as Tag1, that means the
> message M is authenticated.
>
> My questions:
>
> I don't know how tag1 and tag2 were generated but can ensure that they
> will be relevant to message M.
>
> Which possible algorithm / model they used to generate Tag1 and Tag2
> that can make SHA-1 result as expected (matched Tag1), as I know SHA-1 is
> one-way hashing that we can't predict the input that can genrate expected
> output.
>
> --
> You received this message because you are subscribed to a topic in the
> Google Groups "Cryptographic competitions" group.
> To unsubscribe from this topic, visit https://groups.google.com/d/
> topic/crypto-competitions/MgKI6b96T78/unsubscribe.
> To unsubscribe from this group and all its topics, send an email to
> [email protected].
> To post to this group, send email to [email protected].
> Visit this group at https://groups.google.com/group/crypto-competitions.
> For more options, visit https://groups.google.com/d/optout.
>
--
You received this message because you are subscribed to the Google Groups
"Cryptographic competitions" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at https://groups.google.com/group/crypto-competitions.
For more options, visit https://groups.google.com/d/optout.
