<pre>
BIP: 38
Steps performed by ''owner'' to generate a single intermediate code:
#* ownersalt is ''0872b632a22250c5''
#* ownerentropy is ''0872b632a22250c5''
#* passphrase is ''594Y-L2RW-4ME7-2XVX-9B41''
# Derive a key from the passphrase using scrypt
#* Parameters: ''passphrase'' is the passphrase itself encoded in UTF-8 and normalized using Unicode Normalization Form C (NFC). salt is ''ownerentropy''. n=16384, r=8, p=8, length=32.
#* Call the resulting 32 bytes ''prefactor''.
#* prefactor is an alias for ''passfactor''
# Compute the elliptic curve point G * ''passfactor'', and convert the result to compressed notation (33 bytes). Call this ''passpoint''. Compressed notation is used for this purpose regardless of whether the intent is to create Bitcoin addresses with or without compressed public keys.
# Convey ''ownersalt'' and ''passpoint'' to the party generating the keys, along with a checksum to ensure integrity.
#* The following Base58Check-encoded format is recommended for this purpose: magic bytes "2C E9 B3 E1 FF 39 E2 53" followed by ''ownerentropy'', and then ''passpoint''. The resulting string will start with the word "passphrase" due to the constant bytes, will be 72 characters in length, and encodes 49 bytes (8 bytes constant + 8 bytes ''ownerentropy'' + 33 bytes ''passpoint''). The checksum is handled in the Base58Check encoding. The resulting string is called ''intermediate_passphrase_string''.
Steps to create new encrypted private keys given ''intermediate_passphrase_string'' from ''owner'' (so we have ''ownerentropy'', and ''passpoint'', but we do not have ''passfactor'' or the passphrase):
# Set ''flagbyte''.
#* Turn on bit 0x20 if the Bitcoin address will be formed by hashing the compressed public key (optional, saves space, but many Bitcoin implementations aren't compatible with it)
#* Turn on bit 0x04 if ''ownerentropy'' contains a value for ''lotsequence''. (While it has no effect on the keypair generation process, the decryption process needs this flag to know how to process ''ownerentropy'')
# Generate 24 random bytes, call this ''seedb''. Take SHA256(SHA256(''seedb'')) to yield 32 bytes, call this ''factorb''.
# ECMultiply ''passpoint'' by ''factorb''. Use the resulting EC point as a public key and hash it into a Bitcoin address using either compressed or uncompressed public key methodology (specify which methodology is used inside ''flagbyte''). This is the generated Bitcoin address, call it ''generatedaddress''.
# Take the first four bytes of SHA256(SHA256(''generatedaddress'')) and call it ''addresshash''.
# Now we will encrypt ''seedb''. Derive a second key from ''passpoint'' using scrypt
#*Parameters: ''passphrase'' is ''passpoint'' provided from the first party (expressed in binary as 33 bytes). ''salt'' is ''addresshash'' + ''ownerentropy'', n=1024, r=1, p=1, length=64. The "+" operator is concatenation.
#*Split the result into two 32-byte halves and call them ''derivedhalf1'' and ''derivedhalf2''.
# Do AES256Encrypt(block = (seedb[0...15] xor derivedhalf1[0...15]), key = derivedhalf2), call the 16-byte result ''encryptedpart1''
# Do AES256Encrypt(block = ((encryptedpart1[8...15] + seedb[16...23]) xor derivedhalf1[16...31]), key = derivedhalf2), call the 16-byte result ''encryptedpart2''. The "+" operator is concatenation.
The encrypted private key is the Base58Check-encoded concatenation of the following, which totals 39 bytes without Base58 checksum:
* 0x01 0x43 + ''flagbyte'' + ''addresshash'' + ''ownerentropy'' + ''encryptedpart1''[0...7] + ''encryptedpart2''
=====Confirmation code=====
The party generating the Bitcoin address has the option to return a ''confirmation code'' back to ''owner'' which allows ''owner'' to independently verify that he has been given a Bitcoin address that actually depends on his passphrase, and to confirm the lot and sequence numbers (if applicable). This protects ''owner'' from being given a Bitcoin address by the second party that is unrelated to the key derivation and possibly spendable by the second party. If a Bitcoin address given to ''owner'' can be successfully regenerated through the confirmation process, ''owner'' can be reasonably assured that any spending without the passphrase is infeasible. This confirmation code is 75 characters starting with "cfrm38".
To generate it, we need ''flagbyte'', ''ownerentropy'', ''factorb'', ''derivedhalf1'' and ''derivedhalf2'' from the original encryption operation.
# ECMultiply ''factorb'' by G, call the result ''pointb''. The result is 33 bytes.
# The first byte is 0x02 or 0x03. XOR it by (derivedhalf2[31] & 0x01), call the resulting byte ''pointbprefix''.
# Do AES256Encrypt(block = (pointb[1...16] xor derivedhalf1[0...15]), key = derivedhalf2) and call the result ''pointbx1''.
# Do AES256Encrypt(block = (pointb[17...32] xor derivedhalf1[16...31]), key = derivedhalf2) and call the result ''pointbx2''.
# Concatenate ''pointbprefix'' + ''pointbx1'' + ''pointbx2'' (total 33 bytes) and call the result ''encryptedpointb''.
The result is a Base58Check-encoded concatenation of the following:
* 0x64 0x3B 0xF6 0xA8 0x9A + ''flagbyte'' + ''addresshash'' + ''ownerentropy'' + ''encryptedpointb''
A confirmation tool, given a passphrase and a confirmation code, can recalculate the address, verify the address hash, and then assert the following: "It is confirmed that Bitcoin address ''address'' depends on this passphrase". If applicable: "The lot number is ''lotnumber'' and the sequence number is ''sequencenumber''."
To recalculate the address:
# Derive ''passfactor'' using scrypt with ''ownerentropy'' and the user's passphrase and use it to recompute ''passpoint''
# Derive decryption key for ''pointb'' using scrypt with ''passpoint'', ''addresshash'', and ''ownerentropy''
# Decrypt ''encryptedpointb'' to yield ''pointb''
# ECMultiply ''pointb'' by ''passfactor''. Use the resulting EC point as a public key and hash it into ''address'' using either compressed or uncompressed public key methodology as specifid in ''flagbyte''.
=====Decryption=====
# Collect encrypted private key and passphrase from user.
# Derive ''passfactor'' using scrypt with ''ownersalt'' and the user's passphrase and use it to recompute ''passpoint''
# Derive decryption key for ''seedb'' using scrypt with ''passpoint'', ''addresshash'', and ''ownerentropy''
# Decrypt ''encryptedpart2'' using AES256Decrypt to yield the last 8 bytes of ''seedb'' and the last 8 bytes of ''encryptedpart1''.
# Decrypt ''encryptedpart1'' to yield the remainder of ''seedb''.
# Use ''seedb'' to compute ''factorb''.
# Multiply ''passfactor'' by ''factorb'' mod N to yield the private key associated with ''generatedaddress''.
# Convert that private key into a Bitcoin address, honoring the compression preference specified in the encrypted key.
# Hash the Bitcoin address, and verify that ''addresshash'' from the encrypted private key record matches the hash. If not, report that the passphrase entry was incorrect.
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short x = 999; // -32768 to 32767
int x = 99999; // -2147483648 to 2147483647
long x = 99999999999L; // -9223372036854775808 to 9223372036854775807
float x = 1.2;
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Switch is an alternative to If-Else-If ladder and to select one among many blocks of code.
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Collection Framework was introduced since JDK 1.2 which is used to represent and manage Collections and it contains:
This framework also defines map interfaces and several classes in addition to Collections.
| Collection | Description |
|---|---|
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