| 1 | package boxid |
| 2 | |
| 3 | import ( |
| 4 | "bytes" |
| 5 | "crypto/sha256" |
| 6 | "crypto/x509" |
| 7 | "encoding/base64" |
| 8 | "encoding/hex" |
| 9 | "encoding/json" |
| 10 | "errors" |
| 11 | "fmt" |
| 12 | "io" |
| 13 | ) |
| 14 | |
| 15 | // ErrUnverified wraps every reason a record is not evidence for enrollment. |
| 16 | var ErrUnverified = errors.New("boxid: record does not verify") |
| 17 | |
| 18 | // Cloud is the roster entry's cloud field (spec §2, §5.1): the instance a |
| 19 | // box reference is enrolled as. Enrollment fills it from a verified record; |
| 20 | // every later check (the termination fence, volume records) compares |
| 21 | // against it and never against anything a box says about itself. |
| 22 | type Cloud struct { |
| 23 | Provider string `json:"provider"` |
| 24 | Account string `json:"account"` |
| 25 | Region string `json:"region"` |
| 26 | InstanceID string `json:"instance_id"` |
| 27 | } |
| 28 | |
| 29 | // Complete reports whether every field is set and the provider is AWS. |
| 30 | func (c Cloud) Complete() bool { |
| 31 | return c.Provider == "aws" && c.Account != "" && c.Region != "" && c.InstanceID != "" |
| 32 | } |
| 33 | |
| 34 | type Verifier struct { |
| 35 | Account string // the deployment's AWS account id |
| 36 | Certs map[string]*x509.Certificate // by AWS region |
| 37 | } |
| 38 | |
| 39 | // Enrolled is one roster entry as enrollment needs to see it: its |
| 40 | // reference and the instance it was enrolled as. Entries in every state |
| 41 | // count, retired ones included: a retired reference never names a working |
| 42 | // box again (spec §5.9), and a terminated instance never comes back. |
| 43 | type Enrolled struct { |
| 44 | Box string |
| 45 | Cloud Cloud |
| 46 | } |
| 47 | |
| 48 | // Expect is what the enrolling side knows before it reads the record. |
| 49 | type Expect struct { |
| 50 | Box string // the reference being enrolled |
| 51 | AWSRegion string // the AWS region of the placement it is enrolled into |
| 52 | // TofuInstanceID is the region's tofu region-host instance_id output. |
| 53 | // The caller sets it when Box already appears in claims or edges files, |
| 54 | // as a box predating region HA does, and leaves it "" otherwise. |
| 55 | TofuInstanceID string |
| 56 | Roster []Enrolled |
| 57 | } |
| 58 | |
| 59 | // Evidence is what enrollment records: the roster entry's cloud, and the |
| 60 | // SHA-256 of the exact record bytes it was proven from. |
| 61 | type Evidence struct { |
| 62 | Box string |
| 63 | Cloud Cloud |
| 64 | RecordSHA256 string |
| 65 | } |
| 66 | |
| 67 | func refuse(format string, a ...any) error { |
| 68 | return fmt.Errorf("%w: %s", ErrUnverified, fmt.Sprintf(format, a...)) |
| 69 | } |
| 70 | |
| 71 | func decodeRecord(raw []byte) (Record, error) { |
| 72 | dec := json.NewDecoder(bytes.NewReader(raw)) |
| 73 | dec.DisallowUnknownFields() |
| 74 | var rec Record |
| 75 | if err := dec.Decode(&rec); err != nil { |
| 76 | return Record{}, refuse("record is not JSON: %v", err) |
| 77 | } |
| 78 | if _, err := dec.Token(); err != io.EOF { |
| 79 | return Record{}, refuse("trailing data after the record") |
| 80 | } |
| 81 | return rec, nil |
| 82 | } |
| 83 | |
| 84 | // Enroll checks raw, the exact bytes stored at Key(e.Box), as enrollment |
| 85 | // evidence (spec §5.1, H11). In order: the reference, the record's own box |
| 86 | // field, AWS's signature under the certificate for the document's region, |
| 87 | // the deployment account, the AWS region expected for the placement, the |
| 88 | // tofu instance id for a reference predating region HA, and the roster: |
| 89 | // the reference already enrolled as another instance, or the instance |
| 90 | // enrolled under another reference, is refused. A roster entry for the |
| 91 | // reference with no proven cloud yet does not refuse it. A record copied |
| 92 | // from one box to another's key carries the first box's signed instance |
| 93 | // id, so the last check is what keeps one machine from holding two |
| 94 | // references. |
| 95 | // |
| 96 | // The record's box field is not covered by AWS's signature: anything that |
| 97 | // can write the key can name any reference. For a reference the roster |
| 98 | // does not yet hold, Enroll proves only that some instance of the |
| 99 | // deployment wrote the record, so the caller must bind that instance to |
| 100 | // the reference independently (operator approval, the tofu id, or H16's |
| 101 | // group confirmation) before enrolling it. |
| 102 | func (v Verifier) Enroll(raw []byte, e Expect) (Evidence, error) { |
| 103 | if !ValidBox(e.Box) { |
| 104 | return Evidence{}, refuse("%q is not a box reference", e.Box) |
| 105 | } |
| 106 | if e.AWSRegion == "" { |
| 107 | return Evidence{}, refuse("no expected AWS region for %s", e.Box) |
| 108 | } |
| 109 | rec, err := decodeRecord(raw) |
| 110 | if err != nil { |
| 111 | return Evidence{}, err |
| 112 | } |
| 113 | if rec.V != 1 { |
| 114 | return Evidence{}, refuse("record version %d", rec.V) |
| 115 | } |
| 116 | if rec.Box != e.Box { |
| 117 | return Evidence{}, refuse("the record stored for %q names %q", e.Box, rec.Box) |
| 118 | } |
| 119 | doc, err := base64.StdEncoding.DecodeString(rec.IdentityDocument) |
| 120 | if err != nil { |
| 121 | return Evidence{}, refuse("document is not base64") |
| 122 | } |
| 123 | sig, err := base64.StdEncoding.DecodeString(rec.IdentitySignature) |
| 124 | if err != nil { |
| 125 | return Evidence{}, refuse("signature is not base64") |
| 126 | } |
| 127 | var d struct { |
| 128 | AccountID string `json:"accountId"` |
| 129 | Region string `json:"region"` |
| 130 | InstanceID string `json:"instanceId"` |
| 131 | } |
| 132 | if err := json.Unmarshal(doc, &d); err != nil { |
| 133 | return Evidence{}, refuse("document is not JSON") |
| 134 | } |
| 135 | cert := v.Certs[d.Region] |
| 136 | if cert == nil { |
| 137 | return Evidence{}, refuse("no signing certificate for region %q", d.Region) |
| 138 | } |
| 139 | if err := cert.CheckSignature(x509.SHA256WithRSA, doc, sig); err != nil { |
| 140 | return Evidence{}, refuse("signature: %v", err) |
| 141 | } |
| 142 | switch { |
| 143 | case d.InstanceID == "": |
| 144 | return Evidence{}, refuse("document names no instance") |
| 145 | case v.Account == "" || d.AccountID != v.Account: |
| 146 | return Evidence{}, refuse("account %q is not the deployment's", d.AccountID) |
| 147 | case d.Region != e.AWSRegion: |
| 148 | return Evidence{}, refuse("the box is in %q, the placement is in %q", d.Region, e.AWSRegion) |
| 149 | case e.TofuInstanceID != "" && e.TofuInstanceID != d.InstanceID: |
| 150 | return Evidence{}, refuse("tofu records instance %q for this region, the record %q", e.TofuInstanceID, d.InstanceID) |
| 151 | } |
| 152 | for _, en := range e.Roster { |
| 153 | if en.Box == e.Box && en.Cloud.InstanceID != "" && en.Cloud.InstanceID != d.InstanceID { |
| 154 | return Evidence{}, refuse("%s is enrolled as instance %q", e.Box, en.Cloud.InstanceID) |
| 155 | } |
| 156 | if en.Box != e.Box && en.Cloud.InstanceID == d.InstanceID { |
| 157 | return Evidence{}, refuse("instance %s is enrolled as %s", d.InstanceID, en.Box) |
| 158 | } |
| 159 | } |
| 160 | sum := sha256.Sum256(raw) |
| 161 | return Evidence{ |
| 162 | Box: e.Box, |
| 163 | Cloud: Cloud{Provider: "aws", Account: d.AccountID, Region: d.Region, InstanceID: d.InstanceID}, |
| 164 | RecordSHA256: hex.EncodeToString(sum[:]), |
| 165 | }, nil |
| 166 | } |
| 167 | |
amadan