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Store hashed token in DB #707

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Store hashed token in DB #707

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64 changes: 64 additions & 0 deletions auth/token.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,13 @@

import (
"crypto/rand"
"crypto/sha256"
"encoding/hex"
"errors"
"fmt"
"io"
"math/big"
"strings"
)

var (
Expand All @@ -24,6 +30,64 @@
return int(res.Int64())
}

// Convert a Token to its hashed representation.
func HashToken(s string, salt []byte) (string, error) {
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Any reason not using bcrypt like we do for hashing passwords?

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@eternal-flame-AD eternal-flame-AD Oct 23, 2024 •
edited
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It's too expensive and poses a DoS concern.

Tokens are guaranteed to be pseudorandom and have enough entropy, so many of the mitigations by KDFs like bcrypt is not required. The attacker will need to enumerate every possible key to find the result which is usually not true for user-chosen passwords.

Theoretically you can do a bloom filter with a salt or something ... but it is too much effort for the unlikely scenario this original reported attack will have sufficient preconditions to be exploited and not enough preconditions such that the attacker gain no additional practical advantage that they do not already automatically have.

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It's too expensive and poses a DoS concern.

we could use a low strength / iteration count. The big benefit I see we have a prefix we can check if the token is already hashed $2a$ and the salt is already built in. Less code we have to write.

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I don't think we need to salt at all after a second thought. See #707 (comment). We need constant time lookup ourselves. Using any individualized salting (built-in to bcrypt or custom rolled) make this impossible.

saltHex := fmt.Sprintf("%x", salt)
sha := sha256.New()
_, err := sha.Write(salt)
if err != nil {
return "", err
}
_, err = sha.Write([]byte(s))
if err != nil {
return "", err
}
hashed := fmt.Sprintf("%x", sha.Sum(nil))
return fmt.Sprintf("%s$%s", saltHex, hashed), nil
}

// CompareToken compares a token with a hashed representation, optionally upgrading the hash if necessary.
func CompareToken(s string, hashed string) (bool, *string, error) {

Check failure on line 50 in auth/token.go

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if len(s) != randomTokenLength+1 /* prefix */ {
return false, nil, errors.New("invalid token length")
}

split := strings.SplitN(hashed, "$", 2)

// determine if we need to upgrade the hash
if len(split) == 1 {
match := s == hashed
if match {
var salt [16]byte
_, err := io.ReadFull(randReader, salt[:])
if err != nil {
return false, nil, err
}
hashed, err := HashToken(s, salt[:])
if err != nil {
return false, nil, err
}
return true, &hashed, nil
} else {
return false, nil, nil
}
}

if len(split) == 2 {
salt, err := hex.DecodeString(split[0])
if err != nil {
return false, nil, err
}
inputHashed, err := HashToken(s, salt)
if err != nil {
return false, nil, err
}
return inputHashed == hashed, nil, nil
}

return false, nil, errors.New("invalid hash format")
}

// GenerateNotExistingToken receives a token generation func and a func to check whether the token exists, returns a unique token.
func GenerateNotExistingToken(generateToken func() string, tokenExists func(token string) bool) string {
for {
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40 changes: 40 additions & 0 deletions auth/token_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,46 @@ func TestTokenHavePrefix(t *testing.T) {
}
}

func TestHashTokenStable(t *testing.T) {
salt1 := []byte("salt")
salt2 := []byte("pepper")
seen := make(map[string]bool)
for _, plain := range []string{"", "a", "b", "c", "a\x00", "a\n"} {
hash1, err := HashToken(plain, salt1)
assert.NoError(t, err)
hash1Again, err := HashToken(plain, salt1)
assert.NoError(t, err)
assert.Equal(t, hash1, hash1Again)
hash2, err := HashToken(plain, salt2)
assert.NoError(t, err)
hash2Again, err := HashToken(plain, salt2)
assert.NoError(t, err)
assert.Equal(t, hash2, hash2Again)

assert.NotEqual(t, hash1, hash2)
assert.False(t, seen[hash1])
assert.False(t, seen[hash2])
seen[hash1] = true
seen[hash2] = true
}
}

func TestCompareToken(t *testing.T) {
salt := []byte("salt")
tokenPlain := GenerateApplicationToken()
hashed, err := HashToken(tokenPlain, salt)
assert.NoError(t, err)
cmpPlain, upgPlain, err := CompareToken(tokenPlain, tokenPlain)
assert.NoError(t, err)
assert.True(t, cmpPlain)
assert.NotEmpty(t, *upgPlain)

cmpHashed, upgHashed, err := CompareToken(tokenPlain, hashed)
assert.NoError(t, err)
assert.True(t, cmpHashed)
assert.Nil(t, upgHashed)
}

func TestGenerateNotExistingToken(t *testing.T) {
count := 5
token := GenerateNotExistingToken(func() string {
Expand Down
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