HASH.md

(Crypto) Hash

Synonyms (also known as):

• Digital Fingerprint
• Digital Digest
• Digital Checksum

SHA256 - Secure Hash Algorithm 256-Bits

Digest::SHA256.hexdigest( 'Hello, World!' )
#=> "dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f"

Digest::SHA256.hexdigest( 'Hello, World! - Hello, World! - Hello, World! - Hello, World! - Hello, World!' )
#=> "9e513dbdfe60a14f0cac37aeacbe24fa961b428e8ddeb4d6a66006b29425bbd2"

note: 1 hex digit (0-9a-f) = 4 bits; 2 hex digits = 1 byte = 8 bits; always 64 hex digits (0-9a-f) = 32x8 bytes = 256 bits

convert from hex (base 16) to decimal number (base 10)

hex = Digest::SHA256.hexdigest( 'Hello, World!' )
#=> "dffd6021bb2bd5b0af676290809ec3a53191dd81c7f70a4b28688a362182986f"

hex.to_i( 16 )
#=> 101313441018496298855616188252934726526525012911655317211406949275718146758767

convert to 256-bits (32-bytes) binary number (base 2)

h.to_i( 16 ).to_s( 2 )
# => "1101 1111 1111 1101 0110 0000 0010 0001 1011 1011 0010 1011 1101 0101 1011 0000 
#     1010 1111 0110 0111 0110 0010 1001 0000 1000 0000 1001 1110 1100 0011 1010 0101
#     0011 0001 1001 0001 1101 1101 1000 0001 1100 0111 1111 0111 0000 1010 0100 1011
#     0010 1000 0110 1000 1000 1010 0011 0110 0010 0001 1000 0010 1001 1000 0110 1111"

double check (32x8 bytes = 256 bits):

#	bin	hex	#	bin	hex	#	bin	hex	#	bin	hex
1	1101 1111	d f	9	1010 1111	a f	17	0011 0001	3 1	25	0010 1000	2 8
2	1111 1101	f d	10	0110 0111	6 7	18	1001 0001	9 1	26	0110 1000	6 8
3	0110 0000	6 0	11	0110 0010	6 2	19	1101 1101	d d	27	1000 1010	8 a
4	0010 0001	2 1	12	1001 0000	9 0	20	1000 0001	8 1	28	0011 0110	3 6
5	1011 1011	b b	13	1000 0000	8 0	21	1100 0111	c 7	29	0010 0001	2 1
6	0010 1011	2 b	14	1001 1110	9 e	22	1111 0111	f 7	30	1000 0010	8 2
7	1101 0101	d 5	15	1100 0011	c 3	23	0000 1010	0 a	31	1001 1000	9 8
8	1011 0000	b 0	16	1010 0101	a 5	24	0100 1011	4 b	32	0110 1111	6 f

Articles:

• Secure Hash Algorithms @ Wikipedia
• SHA-2 @ Wikipedia - Secure Hash Algorithm 2