challenge/c14.go: refactor

Keep everything inside C14

1 files changed, 103 insertions, 108 deletions

diff --git a/challenge/c14.go b/challenge/c14.go
index 4471f44..552c2df 100644
--- a/challenge/c14.go
+++ b/challenge/c14.go
@@ -9,11 +9,109 @@ import (
 	"ricketyspace.net/cryptopals/lib"
 )
 
-var sheep byte = 65
-
 func C14() {
-	blocksize := findBlockSizeForVarEncryptECB()
-	rpl, nrpb, rpo := findRandPrefixLen(blocksize)
+	sheep := byte(65)
+	freshSheepBytes := func(n int) []byte {
+		in := make([]byte, n)
+		for i := 0; i < n; i++ {
+			in[i] = sheep
+		}
+		return in
+	}
+	findBlockSize := func() int {
+		in := make([]byte, 0)
+
+		in = append(in, sheep)
+		is := len(lib.OracleAESVarEncryptECB(in)) // initial size
+		bs := 0
+		for {
+			in = append(in, sheep)
+			bs = len(lib.OracleAESVarEncryptECB(in))
+			if bs != is {
+				return (bs - is)
+			}
+		}
+	}
+	findPrefixLen := func(blocksize int) (int, int, int) {
+		// Make two sheep blocks.
+		tsb := append(freshSheepBytes(blocksize), freshSheepBytes(blocksize)...)
+
+		v := []byte{}
+		index := 0
+		found := false
+		for {
+			in := append(v, tsb...)
+			c := lib.OracleAESVarEncryptECB(in)
+			index, found = lib.HasConsecutiveMatchingBlocks(c, blocksize)
+			if found {
+				break
+			}
+			// Add another sheep
+			v = append(v, sheep)
+		}
+		l := index - len(v)
+		nrpb := l / blocksize // number of randbox prefix blocks
+		rpo := 0              // random prefix offset
+		if l%blocksize != 0 {
+			nrpb += 1
+			rpo = blocksize - (l % blocksize)
+		}
+		return l, nrpb, rpo
+	}
+	// Finds the cipher block size and the length of the unknown string
+	// (target-bytes).
+	findUnknownStringNumBlocksLength := func(rpl, blocksize int) (int, int) {
+		padding := blocksize - (rpl % blocksize)
+		in := make([]byte, padding)
+		c_sz := len(lib.OracleAESVarEncryptECB(in)) // Cipher size
+
+		nblocks := c_sz / blocksize            // total number of blocks
+		rblocks := (rpl + padding) / blocksize // number of blocks of random prefix
+		ublocks := nblocks - rblocks           // number of blocks of unknown string
+		// Figure out size of unknown string.
+		for {
+			in = append(in, sheep)
+			bs := len(lib.OracleAESVarEncryptECB(in))
+			if bs != c_sz {
+				return ublocks, (c_sz - len(in) - rpl)
+			}
+		}
+	}
+	// `nrpb` number of random prefix blocks
+	// `rpo` random prefix offset
+	// `blocksize` is the size of a block
+	// `block` is the nth block that is being deciphered
+	// `n` is the nth byte of the block `block` that is going to be deciphered.
+	// `in` (n-1)th block that is known
+	// `ds` deciphered unknown string
+	decipherOneByte := func(nrpb, rpo, blocksize, block, n int, in, ds []byte) ([]byte, []byte) {
+		oo := lib.OracleAESVarEncryptECB(in[0:(len(in) - n)])
+
+		s := (nrpb * blocksize) + 16*(block-1)
+		e := s + 16
+		nbl := oo[s:e] // nth block of the cipher
+
+		// Shift `in` to the left by one place.
+		for i := rpo; i < len(in)-1; i++ {
+			in[i] = in[i+1]
+		}
+
+		// Try all combinations.
+		for i := 0; i < 256; i++ {
+			in[len(in)-1] = byte(i)
+			oo = lib.OracleAESVarEncryptECB(in)
+
+			if lib.BlocksEqual(nbl,
+				oo[(nrpb*blocksize):(nrpb*blocksize)+16]) {
+				ds = append(ds, in[len(in)-1])
+				return in, ds
+			}
+		}
+		panic("not found!")
+	}
+
+	blocksize := findBlockSize()
+	rpl, nrpb, rpo := findPrefixLen(blocksize)
 	nbl, us_sz := findUnknownStringNumBlocksLength(
 		rpl, blocksize)
 	in := append(freshSheepBytes(rpo), // random prefix offset
@@ -25,7 +123,7 @@ func C14() {
 			nby = us_sz % blocksize
 		}
 		for j := 0; j < nby; j++ {
-			in, ds = decipherOneByteUS(nrpb, rpo, blocksize,
+			in, ds = decipherOneByte(nrpb, rpo, blocksize,
 				i+1, j+1, in, ds)
 		}
 		s := 16 * i
@@ -35,109 +133,6 @@ func C14() {
 	fmt.Printf("Unknown String:\n%v", lib.BytesToStr(ds))
 }
 
-func freshSheepBytes(n int) []byte {
-	in := make([]byte, n)
-	for i := 0; i < n; i++ {
-		in[i] = sheep
-	}
-	return in
-}
-
-func findBlockSizeForVarEncryptECB() int {
-	in := make([]byte, 0)
-
-	in = append(in, sheep)
-	is := len(lib.OracleAESVarEncryptECB(in)) // initial size
-	bs := 0
-	for {
-		in = append(in, sheep)
-		bs = len(lib.OracleAESVarEncryptECB(in))
-		if bs != is {
-			return (bs - is)
-		}
-	}
-}
-
-func findRandPrefixLen(blocksize int) (int, int, int) {
-	// Make two sheep blocks.
-	tsb := append(freshSheepBytes(blocksize), freshSheepBytes(blocksize)...)
-
-	v := []byte{}
-	index := 0
-	found := false
-	for {
-		in := append(v, tsb...)
-		c := lib.OracleAESVarEncryptECB(in)
-		index, found = lib.HasConsecutiveMatchingBlocks(c, blocksize)
-		if found {
-			break
-		}
-		// Add another sheep
-		v = append(v, sheep)
-	}
-	l := index - len(v)
-	nrpb := l / blocksize // number of randbox prefix blocks
-	rpo := 0              // random prefix offset
-	if l%blocksize != 0 {
-		nrpb += 1
-		rpo = blocksize - (l % blocksize)
-	}
-	return l, nrpb, rpo
-}
-
-// Finds the cipher block size and the length of the unknown string
-// (target-bytes).
-func findUnknownStringNumBlocksLength(rpl, blocksize int) (int, int) {
-	padding := blocksize - (rpl % blocksize)
-	in := make([]byte, padding)
-	c_sz := len(lib.OracleAESVarEncryptECB(in)) // Cipher size
-
-	nblocks := c_sz / blocksize            // total number of blocks
-	rblocks := (rpl + padding) / blocksize // number of blocks of random prefix
-	ublocks := nblocks - rblocks           // number of blocks of unknown string
-	// Figure out size of unknown string.
-	for {
-		in = append(in, sheep)
-		bs := len(lib.OracleAESVarEncryptECB(in))
-		if bs != c_sz {
-			return ublocks, (c_sz - len(in) - rpl)
-		}
-	}
-}
-
-// `nrpb` number of random prefix blocks
-// `rpo` random prefix offset
-// `blocksize` is the size of a block
-// `block` is the nth block that is being deciphered
-// `n` is the nth byte of the block `block` that is going to be deciphered.
-// `in` (n-1)th block that is known
-// `ds` deciphered unknown string
-func decipherOneByteUS(nrpb, rpo, blocksize, block, n int, in, ds []byte) ([]byte, []byte) {
-	oo := lib.OracleAESVarEncryptECB(in[0:(len(in) - n)])
-
-	s := (nrpb * blocksize) + 16*(block-1)
-	e := s + 16
-	nbl := oo[s:e] // nth block of the cipher
-
-	// Shift `in` to the left by one place.
-	for i := rpo; i < len(in)-1; i++ {
-		in[i] = in[i+1]
-	}
-
-	// Try all combinations.
-	for i := 0; i < 256; i++ {
-		in[len(in)-1] = byte(i)
-		oo = lib.OracleAESVarEncryptECB(in)
-
-		if lib.BlocksEqual(nbl,
-			oo[(nrpb*blocksize):(nrpb*blocksize)+16]) {
-			ds = append(ds, in[len(in)-1])
-			return in, ds
-		}
-	}
-	panic("not found!")
-}
-
 // Output:
 // Unknown String:
 // Rollin' in my 5.0