Why does the decode function of the segwit bech32 encoder/decoder take a hrp (human readable part) as input?












1














Looking at the code referenced in bip-0173, specifically for example here:
https://github.com/sipa/bech32/blob/master/ref/javascript/segwit_addr.js



  function decode (hrp, addr) {

      var dec = bech32.decode(addr);

      if (dec === null || dec.hrp !== hrp || dec.data.length < 1 || dec.data[0] > 16) {

        return null;

      }

      ...


I understand that this is an error checking statement, but why check a (user?) inputted hrp vs the decoded hrp from bech32.decode?



Also I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?






segregated-witness bech32-address







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    1














    Looking at the code referenced in bip-0173, specifically for example here:
    https://github.com/sipa/bech32/blob/master/ref/javascript/segwit_addr.js



      function decode (hrp, addr) {
    
      var dec = bech32.decode(addr);
    
      if (dec === null || dec.hrp !== hrp || dec.data.length < 1 || dec.data[0] > 16) {
    
        return null;
    
      }
    
      ...


    I understand that this is an error checking statement, but why check a (user?) inputted hrp vs the decoded hrp from bech32.decode?



    Also I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?






    segregated-witness bech32-address







    share|improve this question

























      1












      1








      1







      Looking at the code referenced in bip-0173, specifically for example here:
      https://github.com/sipa/bech32/blob/master/ref/javascript/segwit_addr.js



        function decode (hrp, addr) {
      
      var dec = bech32.decode(addr);
      
      if (dec === null || dec.hrp !== hrp || dec.data.length < 1 || dec.data[0] > 16) {
      
        return null;
      
      }
      
      ...


      I understand that this is an error checking statement, but why check a (user?) inputted hrp vs the decoded hrp from bech32.decode?



      Also I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?






      segregated-witness bech32-address







      share|improve this question













      Looking at the code referenced in bip-0173, specifically for example here:
      https://github.com/sipa/bech32/blob/master/ref/javascript/segwit_addr.js



        function decode (hrp, addr) {
      
      var dec = bech32.decode(addr);
      
      if (dec === null || dec.hrp !== hrp || dec.data.length < 1 || dec.data[0] > 16) {
      
        return null;
      
      }
      
      ...


      I understand that this is an error checking statement, but why check a (user?) inputted hrp vs the decoded hrp from bech32.decode?



      Also I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?






      segregated-witness bech32-address




      segregated-witness bech32-address






      share|improve this question













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      asked 5 hours ago









      kawthuldrokkawthuldrok

      467




      467






















          2 Answers
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          The HRP is part of the bech32 encoded string, and in the bech32 decoding API, it is returned along with the payload by the decoder, after checking the checksum.



          We still want to compare it with the expected HRP in BIP173, which encodes the chain the software is operating on.



          Otherwise you could have a testnet node that accepts mainnet BIP173 addresses or the other way around.






          share|improve this answer





























            1















            I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?




            No, it's because only versions 0 - 16 are specified. Other versions might behave entirely differently. (As an aside, if it were a comparison for the sake of clamping to the range of a single hex character the test would be >15 not >16).






            share|improve this answer





















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              2 Answers
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              2 Answers
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              3














              The HRP is part of the bech32 encoded string, and in the bech32 decoding API, it is returned along with the payload by the decoder, after checking the checksum.



              We still want to compare it with the expected HRP in BIP173, which encodes the chain the software is operating on.



              Otherwise you could have a testnet node that accepts mainnet BIP173 addresses or the other way around.






              share|improve this answer


























                3














                The HRP is part of the bech32 encoded string, and in the bech32 decoding API, it is returned along with the payload by the decoder, after checking the checksum.



                We still want to compare it with the expected HRP in BIP173, which encodes the chain the software is operating on.



                Otherwise you could have a testnet node that accepts mainnet BIP173 addresses or the other way around.






                share|improve this answer
























                  3












                  3








                  3






                  The HRP is part of the bech32 encoded string, and in the bech32 decoding API, it is returned along with the payload by the decoder, after checking the checksum.



                  We still want to compare it with the expected HRP in BIP173, which encodes the chain the software is operating on.



                  Otherwise you could have a testnet node that accepts mainnet BIP173 addresses or the other way around.






                  share|improve this answer












                  The HRP is part of the bech32 encoded string, and in the bech32 decoding API, it is returned along with the payload by the decoder, after checking the checksum.



                  We still want to compare it with the expected HRP in BIP173, which encodes the chain the software is operating on.



                  Otherwise you could have a testnet node that accepts mainnet BIP173 addresses or the other way around.







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 4 hours ago









                  Pieter WuillePieter Wuille

                  45.6k393154




                  45.6k393154























                      1















                      I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?




                      No, it's because only versions 0 - 16 are specified. Other versions might behave entirely differently. (As an aside, if it were a comparison for the sake of clamping to the range of a single hex character the test would be >15 not >16).






                      share|improve this answer


























                        1















                        I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?




                        No, it's because only versions 0 - 16 are specified. Other versions might behave entirely differently. (As an aside, if it were a comparison for the sake of clamping to the range of a single hex character the test would be >15 not >16).






                        share|improve this answer
























                          1












                          1








                          1







                          I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?




                          No, it's because only versions 0 - 16 are specified. Other versions might behave entirely differently. (As an aside, if it were a comparison for the sake of clamping to the range of a single hex character the test would be >15 not >16).






                          share|improve this answer













                          I'm assuming that the "dec.data[0] > 16" check is to make sure that the byte at index zero doesn't exceed a value of 16, which would be invalid hex. Is this correct?




                          No, it's because only versions 0 - 16 are specified. Other versions might behave entirely differently. (As an aside, if it were a comparison for the sake of clamping to the range of a single hex character the test would be >15 not >16).







                          share|improve this answer












                          share|improve this answer



                          share|improve this answer










                          answered 4 hours ago









                          G. MaxwellG. Maxwell

                          3,3821630




                          3,3821630






























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