# How can I determine the GPG/PGP key ID from the RSA modulus?

According to http://www.pgp.net/pgpnet/pgp-faq/pgp-faq-keys.html#key-public-key-forgery, key ID is some lower bits sequence from the modulus (i.e. the $n$ variable):

A PGP key ID is just the bottom 64 bits of the public modulus (but only the bottom 32 bits are displayed with pgp -kv).

I have a key pair. According to pgpdump, my key ID (i.e. 64b) is the following one 0x6BA09C369E31148C. According to GPG, my key ID (i.e. 32b) is the following one: 0x9E31148C. Well, this is just the last 32 bits from the 64b key ID.

I'd like to see a relation to my public modulus. I haven't found any, even if I play with endianess.

The key id is also weird… if it was last 32b (or 64b) from the modulus, it should be an odd number (except if $p$ == $2$ || $q == 2$\$, which is very unlikely).

However, when I search lower 32 bits in my modulus (dumped by pgpdump), I see 0x84cfe5c1, which is far different from 0x9E31148C:

RSA n(4096 bits) - c8 1a 2e 7d e5 22 84 5c 10 b9 02 3b 42 ff 09 4c 60 f9 8a ce 80 64 8a 95 6a 0e 53 23 a3 dc fb fb f5 96 c7 a2 de be a9 f0 c8 f8 d8 51
6d e8 bc 64 13 16 5e 25 f9 4d 44 bc 51 ef 7f 97 b4 05 a3 d9 9e e3 58 ef 88 c1 bb e5 23 65 45 1b 99 7b 68 c1 e4 1a 7d bc fb 51 c1 41 d6 10 33 34 90 c3 91 5c 5b
ae 48 63 4e 65 46 4e 35 8e 48 e6 85 e3 9b ff b2 4b e9 c6 aa f1 45 3f b8 b6 b5 be 56 f8 04 4e 1d 1a d4 78 4d 75 fa 5e aa 2d 6d dc 31 2b c8 28 db cb 10 34 1a 16
2c fd e2 67 e7 1d 0b e6 cc 53 92 5d 85 40 57 5c 9f 23 bb af 75 d9 11 2b 4a a0 6c ef c4 50 85 eb 79 46 b2 f7 03 54 8a c9 15 c0 ac d8 d4 5a 7c 5e 37 5e cc f2 13
8a 67 3c 1f 26 c5 f4 11 d0 38 19 9c 34 0f c0 3d e7 63 67 8e 3f 7d 82 2e b6 59 d3 da 74 61 68 1c 78 7b 4c ce c3 5a f0 18 8c 3b ab 3c 88 03 28 6b 93 f5 b9 eb eb
44 51 a7 b8 34 08 e9 a7 fa 81 d3 af 3d a0 f7 fa 6b f9 fb 98 97 38 32 d1 1f e4 e7 1a 4d af e3 e9 87 f8 ca b1 10 91 e5 9c fc db 4b 2d 23 3a 3f c3 fc 1b fe 15 c1
df ff a2 0e fb 51 fe c3 1c 67 26 f3 f3 9d 50 ff 8b a7 48 f4 57 1c e8 63 e9 1e 1b 4a 27 96 02 9c 06 5a 62 ed 99 80 02 13 b2 31 66 a8 ee 79 15 85 05 61 81 67 0f
b7 c6 4e d9 5f 31 81 64 d7 16 13 a8 70 a5 26 6f dc c3 cd f7 d3 8a 3d ab 79 60 34 6d 4e 9b f7 ef 32 eb 65 75 63 f4 79 1c 43 a8 ae 64 53 fd 56 77 d4 df 68 1e b6
05 b0 d1 1d 7c fc 10 5a a3 aa eb 90 90 a8 6d 15 a6 8c 03 85 97 7b 0f 15 fe 19 07 ff 12 ff 10 87 fe bb 85 7b d3 98 34 24 8e c0 cb 5f 9a 42 81 71 76 3c fc 2d fb
55 40 98 56 b0 b6 bd 26 8d bd 66 86 9a b2 49 cf a8 0f 4d 3c ed 62 34 79 4f 98 bd 5c 73 dc e5 45 cf 3f e0 a6 4a 59 e2 09 84 cf e5 c1


Where is the mistake in understanding the Key ID?

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