How can I apply hash on a string.

How can i apply hash function on a string and reverse process to generate the same string from the hash value.

Answer 1

[Ameer Hamza]

Hashing is not a reversible process. You can do encoding and decoding. For example

A = 'The quick brown fox jumps over the lazy dog';

encoded_str = matlab.net.base64encode(A);
decoded_str = char(matlab.net.base64decode(encoded_str));

Result

>> encoded_str
encoded_str =
    'VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZw=='
>> decoded_str
decoded_str =
    'The quick brown fox jumps over the lazy dog'

[Balkar Singh]

The length of string A is 44 while the length of encoded string is 60. Can we find the relation between the both length.

[Ameer Hamza]

You can read more about the encoding here: https://tools.ietf.org/html/rfc4648#section-4. The number of characters in an encoded string is given by

A = 'Ameer Hamza KhanTmer the lazy dog';
encoded_str = matlab.net.base64encode(A);

n1 = numel(encoded_str);
n2 = ceil(numel(A)/3)*4;

Result:

>> n1
n1 =
    60
>> n2
n2 =
    60

[Balkar Singh]

Thanks sir

s3 = containers.Map({'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','1','2','3','4','5','6','7','8','9',' ','!'},{'110000','110001','110010','110011','110100','110101','110110','110111','111000','111001','111010','111011','111100','111101','111110','111111','000000','000001','000010','000011','000100','000101','000110','000111','001000','001001','010000','010001','010010','010011','010100','010101','010110','010111','011000','011001','011010','011011','011100','011101','011110','011111','100000','100001','100010','100011','100100','100101','100110','100111','101000','101001','001011','001100','001101','001110','001111','101010','101011','101100','101101','101110','101111'});

When i compare the encoded_str with this container.I got the following error

Error using containers.Map/subsref

Specified key type does not match the type expected for this container.

what is the solution of this problem.

[Ameer Hamza]

Can you show which line gives this error?

[Balkar Singh]

Thanks sir..I solved it.

[Balkar Singh]

s3 = containers.Map({'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','1','2','3','4','5','6','7','8','9','','!','0'},{'110000','110001','110010','110011','110100','110101','110110','110111','111000','111001','111010','111011','111100','111101','111110','111111','000000','000001','000010','000011','000100','000101','000110','000111','001000','001001','010000','010001','010010','010011','010100','010101','010110','010111','011000','011001','011010','011011','011100','011101','011110','011111','100000','100001','100010','100011','100100','100101','100110','100111','101000','101001','001011','001100','001101','001110','001111','101010','101011','101100','101101','101110','101111','001010'});
encoded_str=mlreportgen.utils.hash(cover_str);
i=1;
cnt = length(encoded_str);
HBS='';
while(cnt>0)
     encoded_str(1,i)
     val=s3(encoded_str(1,i))  Error occured here
     i=i+1
     cnt = cnt-1;   
     %input("Hello")
     HBS=strcat(HBS,val);
end

Error using containers.Map/subsref

The specified key is not present in this container.

[Ameer Hamza]

What value of cover_str are you using?

[Balkar Singh]

cover_str = 'Most teachers waste their time by asking questions that are indended to discover what the pupil does not know, whereas the true art of questioning is to discover what the pupil does know or is capable of knowing.';  

[Ameer Hamza]

Balkar, mlreportgen.utils.hash returns a string, which is different from char array in MATLAB. length(encoded_str) returns 1 always. Change it to char array by changing the line

encoded_str=mlreportgen.utils.hash(cover_str);

to

encoded_str=char(mlreportgen.utils.hash(cover_str));

[Balkar Singh]

OK sir..Thank you very much