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Refactor common STR verification functionality (#170)
* Add client-auditor messages * Add client-auditor messages * Create audit log structure, query API finished * Add/Update docs to include auditor, add ReqUnknownDirectory auditor error * Use single generic verifySTRConsistency to be used by client and auditor * Add tests for audit log, debug audit log * Add assertions to validate auditor messages on client * Add generic STR response handler * Add TODO to move all generic STR auditing code to a separate module * [WIP] Refactor generic auditing functionality * Add client-auditor messages * Create audit log structure, query API finished * Add/Update docs to include auditor, add ReqUnknownDirectory auditor error * Use single generic verifySTRConsistency to be used by client and auditor * Add tests for audit log, debug audit log * Add assertions to validate auditor messages on client * Add generic STR response handler * # This is a combination of 2 commits. # The first commit's message is: Add TODO to move all generic STR auditing code to a separate module # The 2nd commit message will be skipped: # Use single generic verifySTRConsistency to be used by client and auditor * Fix documentation * Use DirSTR instead of merkletree.SignedTreeRoot in auditlog * Remove all references to auditor-directory communication, make auditor response message generic * STRList -> STRHistoryRange * Fail sooner in GetObservedSTRs * Revert changes to protocol/str.go * Always request epoch range in AuditingRequest, fix Insert() bug * Index audit log by hash of directory's initial STR * Insert latest STR into snapshot map right away * Fix go vet error * Change audit log index from byte array to string * Add test case for getting an STR after an audit log update * Refactor common functions * Create generic auditor interface * Fix go fmt * Fix some merging issues * Refactor generic auditing functionality TODO: * Add tests * Renaming STR verification functions, use generic auditor functionality in auditlog and consistencychecks * h.verifiedSTR -> h.VerifiedSTR() * Refactor common STR verification for STR ranges from server * Fix * Fix documentation and formatting, revert to use map for auditlog snapshots * Minor fixes * Minor fix * Typo * Part of #151
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,174 @@ | ||
| // This module implements a generic CONIKS auditor, i.e. the | ||
| // functionality that clients and auditors need to verify | ||
| // a server's STR history. | ||
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| package protocol | ||
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| import ( | ||
| "fmt" | ||
| "reflect" | ||
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| "github.com/coniks-sys/coniks-go/crypto" | ||
| "github.com/coniks-sys/coniks-go/crypto/sign" | ||
| ) | ||
|
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| // Auditor provides a generic interface allowing different | ||
| // auditor types to implement specific auditing functionality. | ||
| type Auditor interface { | ||
| AuditDirectory([]*DirSTR) error | ||
| } | ||
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| // AudState verifies the hash chain of a specific directory. | ||
| type AudState struct { | ||
| signKey sign.PublicKey | ||
| verifiedSTR *DirSTR | ||
| } | ||
|
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| var _ Auditor = (*AudState)(nil) | ||
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| // NewAuditor instantiates a new auditor state from a persistance storage. | ||
| func NewAuditor(signKey sign.PublicKey, verified *DirSTR) *AudState { | ||
| a := &AudState{ | ||
| signKey: signKey, | ||
| verifiedSTR: verified, | ||
| } | ||
| return a | ||
| } | ||
|
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| // VerifiedSTR returns the newly verified STR. | ||
| func (a *AudState) VerifiedSTR() *DirSTR { | ||
| return a.verifiedSTR | ||
| } | ||
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| // Update updates the auditor's verifiedSTR to newSTR | ||
| func (a *AudState) Update(newSTR *DirSTR) { | ||
| a.verifiedSTR = newSTR | ||
| } | ||
|
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| // compareWithVerified checks whether the received STR is the same as | ||
| // the verified STR in the AudState using reflect.DeepEqual(). | ||
| func (a *AudState) compareWithVerified(str *DirSTR) error { | ||
| if reflect.DeepEqual(a.verifiedSTR, str) { | ||
| return nil | ||
| } | ||
| return CheckBadSTR | ||
| } | ||
|
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| // verifySTRConsistency checks the consistency between 2 snapshots. | ||
| // It uses the signing key signKey to verify the STR's signature. | ||
| // The signKey param either comes from a client's | ||
| // pinned signing key in its consistency state, | ||
| // or an auditor's pinned signing key in its history. | ||
| func (a *AudState) verifySTRConsistency(prevSTR, str *DirSTR) error { | ||
| // verify STR's signature | ||
| if !a.signKey.Verify(str.Serialize(), str.Signature) { | ||
| return CheckBadSignature | ||
| } | ||
| if str.VerifyHashChain(prevSTR) { | ||
| return nil | ||
| } | ||
|
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| // TODO: verify the directory's policies as well. See #115 | ||
| return CheckBadSTR | ||
| } | ||
|
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| // checkSTRAgainstVerified checks an STR str against the a.verifiedSTR. | ||
| // If str's Epoch is the same as the verified, checkSTRAgainstVerified() | ||
| // compares the two STRs directly. If str is one epoch ahead of the | ||
| // a.verifiedSTR, checkSTRAgainstVerified() checks the consistency between | ||
| // the two STRs. | ||
| // checkSTRAgainstVerified() returns nil if the check passes, | ||
| // or the appropriate consistency check error if any of the checks fail, | ||
| // or str's epoch is anything other than the same or one ahead of | ||
| // a.verifiedSTR. | ||
| func (a *AudState) checkSTRAgainstVerified(str *DirSTR) error { | ||
| // FIXME: check whether the STR was issued on time and whatnot. | ||
| // Maybe it has something to do w/ #81 and client | ||
| // transitioning between epochs. | ||
| // Try to verify w/ what's been saved | ||
|
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| // FIXME: we are returning the error immediately | ||
| // without saving the inconsistent STR | ||
| // see: https://github.com/coniks-sys/coniks-go/pull/74#commitcomment-19804686 | ||
| switch { | ||
| case str.Epoch == a.verifiedSTR.Epoch: | ||
| // Checking an STR in the same epoch | ||
| if err := a.compareWithVerified(str); err != nil { | ||
| return err | ||
| } | ||
| case str.Epoch == a.verifiedSTR.Epoch+1: | ||
| // Otherwise, expect that we've entered a new epoch | ||
| if err := a.verifySTRConsistency(a.verifiedSTR, str); err != nil { | ||
| return err | ||
| } | ||
| default: | ||
| return CheckBadSTR | ||
| } | ||
|
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| return nil | ||
| } | ||
|
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| // verifySTRRange checks the consistency of a range | ||
| // of a directory's STRs. It begins by verifying the STR consistency between | ||
| // the given prevSTR and the first STR in the given range, and | ||
| // then verifies the consistency between each subsequent STR pair. | ||
| func (a *AudState) verifySTRRange(prevSTR *DirSTR, strs []*DirSTR) error { | ||
| prev := prevSTR | ||
| for i := 0; i < len(strs); i++ { | ||
| str := strs[i] | ||
| if str == nil { | ||
| // FIXME: if this comes from the auditor, this | ||
| // should really be an ErrMalformedAuditorMessage | ||
| return ErrMalformedDirectoryMessage | ||
| } | ||
|
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| // verify the consistency of each STR in the range | ||
| if err := a.verifySTRConsistency(prev, str); err != nil { | ||
| return err | ||
| } | ||
|
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| prev = str | ||
| } | ||
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| return nil | ||
| } | ||
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| // AuditDirectory validates a range of STRs received from a CONIKS directory. | ||
| // AuditDirectory() checks the consistency of the oldest STR in the range | ||
| // against the verifiedSTR, and verifies the remaining | ||
| // range if the message contains more than one STR. | ||
| // AuditDirectory() returns the appropriate consistency check error | ||
| // if any of the checks fail, or nil if the checks pass. | ||
| func (a *AudState) AuditDirectory(strs []*DirSTR) error { | ||
| // validate strs | ||
| if len(strs) == 0 { | ||
| return ErrMalformedDirectoryMessage | ||
| } | ||
|
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| // check STR against the latest verified STR | ||
| if err := a.checkSTRAgainstVerified(strs[0]); err != nil { | ||
| return err | ||
| } | ||
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| // verify the entire range if we have received more than one STR | ||
| if len(strs) > 1 { | ||
| if err := a.verifySTRRange(strs[0], strs[1:]); err != nil { | ||
| return err | ||
| } | ||
| } | ||
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| return nil | ||
| } | ||
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| // ComputeDirectoryIdentity returns the hash of | ||
| // the directory's initial STR as a byte array. | ||
| // It panics if the STR isn't an initial STR (i.e. str.Epoch != 0). | ||
| func ComputeDirectoryIdentity(str *DirSTR) [crypto.HashSizeByte]byte { | ||
| if str.Epoch != 0 { | ||
| panic(fmt.Sprintf("[coniks] Expect epoch 0, got %x", str.Epoch)) | ||
| } | ||
|
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| var initSTRHash [crypto.HashSizeByte]byte | ||
| copy(initSTRHash[:], crypto.Digest(str.Signature)) | ||
| return initSTRHash | ||
| } |
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