How to Encode String (Use Encrypt Messagedigest in Java) to Base64 String in Swift

How to encode string (use encrypt MessageDigest in Java) to Base64 string in swift?

Your code does not produce the expected result because the
referenced md5() function returns the message digest as a
hex-encoded string, which is then Base64 encoded. So instead of

 String -> UTF-8 data -> MD5 digest -> Base64 encoding

you are doing

 String -> UTF-8 data -> MD5 digest -> hex encoding -> Base64 encoding

A small modification of the function returns the message digest
as data:

func md5(string string: String) -> NSData {
    var digest = [UInt8](count: Int(CC_MD5_DIGEST_LENGTH), repeatedValue: 0)
    let data = string.dataUsingEncoding(NSUTF8StringEncoding)! // Conversion to UTF-8 cannot fail
    CC_MD5(data.bytes, CC_LONG(data.length), &digest)
    return NSData(bytes: digest, length: digest.count)
}

Now you can compute the Base 64 encoded MD5 digest:

let string = "Hello World"

// Compute MD5 message digest:
let md5data = md5(string: string)
print("md5data = \(md5data)") // md5data = <b10a8db1 64e07541 05b7a99b e72e3fe5>

// Convert to Base 64 encoded string:
let base64 = md5data.base64EncodedStringWithOptions([])
print("base64 = \(base64)") // base64 = sQqNsWTgdUEFt6mb5y4/5Q==

This is almost what you expect. The Java code apparently produces
the so-called "base64url" variant without padding
(compare https://en.wikipedia.org/wiki/Base64#Variants_summary_table).

Therefore we have to modify two characters and remove the padding:

let base64url = base64
    .stringByReplacingOccurrencesOfString("+", withString: "-")
    .stringByReplacingOccurrencesOfString("/", withString: "_")
    .stringByReplacingOccurrencesOfString("=", withString: "")
print("base64url = \(base64url)") // base64url = sQqNsWTgdUEFt6mb5y4_5Q

Now the result is sQqNsWTgdUEFt6mb5y4_5Q, and identical to what
you got from the Java code.

Convert UIImage to base64 string in swift

Do it something like this:

For Encoding:

data.base64EncodedStringWithOptions([])

For decoding:

let url = URL(string: String(format:"data:application/octet-stream;base64,%@",base64String))
do {
    let data =  try Data(contentsOf: url!)
}catch {

}

iOS CryptoKit in Java

This is the final set of code in SWIFT:

let pass = “Password”
let data = “Text to encrypt”.data(using: .utf8)!
let key = SymmetricKey(data: SHA256.hash(data: pass.datat(using: .utf8)!))
let iv = AES.GCM.Nonce()
let mySealedBox = try AES.GCM.seal(data, using: key, nonce: iv)
dataToShare = mySealedBox.combined?.base64EncodedData()

Write this data to a file (I am using google APIs to write this data to a file on google drive)

Read this data from the file in java and pass it to the functions as defined in the question using the below code:

byte[] iv = Base64.getDecoder().decode(text.substring(0,16));
cipher[] = Base64.getDecoder().decode(text.substring(16));
byte[] key = md.digest(pass.getBytes(StandardCharsets.UTF_8));
String plainText = decrypt(cipher, key, iv);

How to decrypt a SHA-256 encrypted string?

SHA-256 is a cryptographic (one-way) hash function, so there is no direct way to decode it. The entire purpose of a cryptographic hash function is that you can't undo it.

One thing you can do is a brute-force strategy, where you guess what was hashed, then hash it with the same function and see if it matches. Unless the hashed data is very easy to guess, it could take a long time though.

You may find the question "Difference between hashing a password and encrypting it" interesting.

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