We encrypt RndA||RndB’ and send this to the tag with a command byte of AF + our enc(RndA||RndB’) = 62 7a b7 02 0c fe c7 8b a2 4e 6b 43 5e 0f a0 b7.Concatenate RndB’ with Rnd A =9b 75 fe 7f 5b 9e ba 79 46 86 a9 4b f7 94 cd 13.Next we generate our own random number (if we wish) RndA =9b 75 fe 7f 5b 9e ba 79.We decrypt these bytes to get the real number RndB’ =13 46 86 a9 4b f7 94 cd.This e_k(RndB), is an encrypted Random number with key k.

The card/tag responds with AF followed by 8 bytes e_k(RndB) and a 2 byte CRC.

The authentication starts with the command 1A 00 concatenated with an iso1433a CRC.

Start = Start of Start Bit, End = End of last modulation.

Auth1 controls the enforced restrictions 0x1 = Read Unauthenticated & Write Protected 0x00 = Read & Write Protectedīelow is a trace of attempted authentication with an Ultralight C card: proxmark3> hf mfu auth.

Auth0 controls the page range from 0x03 – 0x30 (0x00 = disabled).

Basically a 3DES (Triple DES) key (16 bytes split into key 1 and key2, (ke圓=key1)) is used for Authentication Only! Depending on the configuration of Auth0 & Auth1 Page/Block (2a byte 0 & b Byte 0) depends on what pages/blocks are accessible. proxmark3> hf mfu ucrdcardĬontrary to belief (I admit making an initial mistake here), Ultralight C contents are not encrypted by default! (Unless cryptography has been added by the controlling application). The remaining 4 blocks contain the 3DES Key needed for authentication, and are write only, so the key cannot be simply recovered.

The Card has 0x2f Pages (or blocks) which means 47 decimal blocks.

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