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AwsCryptographyDbEncryptionSdkDynamoDbItemEncryptorOperations.dfy
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// Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0
include "../../DynamoDbEncryption/src/DynamoToStruct.dfy"
include "Util.dfy"
include "InternalLegacyOverride.dfy"
include "../../StructuredEncryption/src/Util.dfy"
module AwsCryptographyDbEncryptionSdkDynamoDbItemEncryptorOperations refines AbstractAwsCryptographyDbEncryptionSdkDynamoDbItemEncryptorOperations {
import ComAmazonawsDynamodbTypes
import opened DynamoDbItemEncryptorUtil
import CMP = AwsCryptographyMaterialProvidersTypes
import StructuredEncryption
import DynamoToStruct
import SortedSets
import Base64
import opened StandardLibrary
import Seq
import CSE = AwsCryptographyDbEncryptionSdkStructuredEncryptionTypes
import SE = StructuredEncryptionUtil
import InternalLegacyOverride
import MaterialProviders
import RequiredEncryptionContextCMM
import SET = AwsCryptographyDbEncryptionSdkStructuredEncryptionTypes
import DDBE = AwsCryptographyDbEncryptionSdkDynamoDbTypes
import StandardLibrary.String
import StructuredEncryptionHeader
datatype Config = Config(
nameonly version : StructuredEncryptionHeader.Version,
nameonly cmpClient : MaterialProviders.MaterialProvidersClient,
nameonly logicalTableName: string,
nameonly partitionKeyName: ComAmazonawsDynamodbTypes.KeySchemaAttributeName,
nameonly sortKeyName: Option<ComAmazonawsDynamodbTypes.KeySchemaAttributeName>,
nameonly cmm: CMP.ICryptographicMaterialsManager,
nameonly attributeActionsOnEncrypt: DDBE.AttributeActions,
nameonly allowedUnsignedAttributes: Option<ComAmazonawsDynamodbTypes.AttributeNameList>,
nameonly allowedUnsignedAttributePrefix: Option<string>,
nameonly algorithmSuiteId: Option<CMP.DBEAlgorithmSuiteId>,
nameonly structuredEncryption: StructuredEncryption.StructuredEncryptionClient,
nameonly plaintextOverride: DDBE.PlaintextOverride,
nameonly internalLegacyOverride: Option<InternalLegacyOverride.InternalLegacyOverride> := None
)
type InternalConfig = Config
type ValidConfig = x : Config | ValidInternalConfig?(x) witness *
// Is the attribute name an allowed unauthenticated name?
predicate method AllowedUnsigned(
unauthenticatedAttributes: Option<ComAmazonawsDynamodbTypes.AttributeNameList>,
unauthenticatedPrefix: Option<string>,
attr : string)
{
|| (unauthenticatedAttributes.Some? && attr in unauthenticatedAttributes.value)
|| (unauthenticatedPrefix.Some? && unauthenticatedPrefix.value <= attr)
|| ReservedPrefix <= attr
// Attributes with the reserved prefix are "allowed unauthenticated" in that
// they are not specified as signed within attributeActionsOnEncrypt.
// These attributes MAY still be authenticated via other methods,
// such as "aws_dbe_head" which is explicitly added to the canonical hash
// used in signing.
}
//= specification/dynamodb-encryption-client/decrypt-item.md#signature-scope
//= type=implication
//# If an Authenticate Action other than DO_NOTHING is configured for an attribute name included in [Unauthenticated Attributes](./ddb-table-encryption-config.md#unauthenticated-attributes)
//# or beginning with the prefix specified in [Unauthenticated Attribute Prefix](./ddb-table-encryption-config.md#unauthenticated-attribute-prefix),
//# this operation MUST yield an error.
// This is used only in ValidInternalConfig?
predicate method ForwardCompatibleAttributeAction(
attribute: string,
action: CSE.CryptoAction,
unauthenticatedAttributes: Option<ComAmazonawsDynamodbTypes.AttributeNameList>,
unauthenticatedPrefix: Option<string>
)
{
if action == CSE.DO_NOTHING then
AllowedUnsigned(unauthenticatedAttributes, unauthenticatedPrefix, attribute)
else
!AllowedUnsigned(unauthenticatedAttributes, unauthenticatedPrefix, attribute)
}
function method CryptoActionString(action: CSE.CryptoAction) : string
{
if action == CSE.DO_NOTHING then
"DO_NOTHING"
else if action == CSE.SIGN_ONLY then
"SIGN_ONLY"
else if action == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT then
"SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT"
else if action == CSE.ENCRYPT_AND_SIGN then
"ENCRYPT_AND_SIGN"
else
assert false by {
assert action != CSE.DO_NOTHING;
assert action != CSE.SIGN_ONLY;
assert action != CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT;
assert action != CSE.ENCRYPT_AND_SIGN;
}
"internal error"
}
function method ExplainNotForwardCompatible(
attr: string,
action: CSE.CryptoAction,
unauthenticatedAttributes: Option<ComAmazonawsDynamodbTypes.AttributeNameList>,
unauthenticatedPrefix: Option<string>
)
: string
requires !ForwardCompatibleAttributeAction(attr, action, unauthenticatedAttributes, unauthenticatedPrefix)
{
"Attribute " + attr + " is configured as " + CryptoActionString(action) + " but " +
if action == CSE.DO_NOTHING then
"it must also be in unauthenticatedAttributes or begin with the unauthenticatedPrefix."
else if unauthenticatedAttributes.Some? && attr in unauthenticatedAttributes.value then
"it is also in unauthenticatedAttributes."
else if unauthenticatedPrefix.Some? && unauthenticatedPrefix.value <= attr then
"it also begins with the unauthenticatedPrefix."
else
assert ReservedPrefix <= attr;
"it also begins with the reserved prefix."
}
// Is this attribute unknown to the config?
predicate method UnknownAttribute(config : InternalConfig, attr : ComAmazonawsDynamodbTypes.AttributeName)
{
&& InSignatureScope(config, attr)
&& attr !in config.attributeActionsOnEncrypt
// Attributes in signature scope MUST be configured in attributeActionsOnEncrypt
// so these two lines are saying "in scope && not in scope"
// and that's why it's an error
}
// Is the attribute name in signature scope?
predicate method InSignatureScope(config : InternalConfig, attr : ComAmazonawsDynamodbTypes.AttributeName)
{
!AllowedUnsigned(
config.allowedUnsignedAttributes,
config.allowedUnsignedAttributePrefix,
attr)
}
function method EncodeName(k : string) : (ret : Result<UTF8.ValidUTF8Bytes, Error>)
ensures ret == DDBEncode(SE.ATTR_PREFIX + k)
{
DDBEncode(SE.ATTR_PREFIX + k)
}
function method MakeEncryptionContextForEncrypt(
config : InternalConfig,
item : DynamoToStruct.TerminalDataMap)
: (ret : Result<CMP.EncryptionContext, Error>)
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context
//= type=implication
//# If the [Configuration Version](./ddb-table-encryption-config.md#configuration-version) is 2,
//# then the base context MUST be the [version 2](#dynamodb-item-base-context-version-2) context;
//# otherwise, the base context MUST be the [version 1](#dynamodb-item-base-context-version-1) context.
ensures config.version == 2 ==> ret == MakeEncryptionContextV2(config, item)
ensures config.version == 1 ==> ret == MakeEncryptionContextV1(config, item)
ensures (config.version == 1) || (config.version == 2)
{
if config.version == 2 then
MakeEncryptionContextV2(config, item)
else
MakeEncryptionContextV1(config, item)
}
function method MakeEncryptionContextForDecrypt(
config : InternalConfig,
header : seq<uint8>,
item : DynamoToStruct.TerminalDataMap)
: (ret : Result<CMP.EncryptionContext, Error>)
requires 0 < |header|
ensures ret.Success? ==>
//= specification/dynamodb-encryption-client/decrypt-item.md#dynamodb-item-base-context
//= type=implication
//# If the Version Number is 2, then the base context MUST be the [version 2](./encrypt-item.md#dynamodb-item-base-context-version-2) context.
&& (header[0] == 2 ==> ret == MakeEncryptionContextV2(config, item))
//= specification/dynamodb-encryption-client/decrypt-item.md#dynamodb-item-base-context
//= type=implication
//# If the Version Number is 1, the base context MUST be the [version 1](./encrypt-item.md#dynamodb-item-base-context-version-1) context.
&& (header[0] == 1 ==> ret == MakeEncryptionContextV1(config, item))
&& ((header[0] == 1) || (header[0] == 2))
//= specification/dynamodb-encryption-client/decrypt-item.md#dynamodb-item-base-context
//= type=implication
//# If the Version Number is not 1 or 2, the operation MUST return an error.
ensures ((header[0] != 1) && (header[0] != 2)) ==> ret.Failure?
{
if header[0] == 2 then
MakeEncryptionContextV2(config, item)
else if header[0] == 1 then
MakeEncryptionContextV1(config, item)
else
Failure(E("Header attribute has unexpected version number"))
}
function method {:opaque} {:vcs_split_on_every_assert} MakeEncryptionContextV1(
config : InternalConfig,
item : DynamoToStruct.TerminalDataMap)
: (ret : Result<CMP.EncryptionContext, Error>)
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context-version-1
//= type=implication
//# The DynamoDB Item Base Context MUST contain:
//# - the key "aws-crypto-table-name" with a value equal to the configured
//# [logical table name](./ddb-table-encryption-config.md#logical-table-name).
//# - the key "aws-crypto-partition-name" with a value equal to the name of the Partition Key on this item.
//# - the [value](#base-context-value-version-1) of the Partition Key.
ensures ret.Success? ==>
&& config.partitionKeyName in item
&& TABLE_NAME in ret.value
&& DDBEncode(config.logicalTableName).Success?
&& var logicalTableName : ValidUTF8Bytes := DDBEncode(config.logicalTableName).value;
&& ret.value[TABLE_NAME] == logicalTableName
&& PARTITION_NAME in ret.value
&& DDBEncode(config.partitionKeyName).Success?
&& var partitionName : ValidUTF8Bytes := DDBEncode(config.partitionKeyName).value;
&& ret.value[PARTITION_NAME] == partitionName
&& EncodeName(config.partitionKeyName).Success?
&& var partitionKeyName : ValidUTF8Bytes := EncodeName(config.partitionKeyName).value;
&& var partitionKeyValue : ValidUTF8Bytes := SE.EncodeTerminal(item[config.partitionKeyName]);
&& partitionKeyName in ret.value
&& ret.value[partitionKeyName] == partitionKeyValue
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context-version-1
//= type=implication
//# If this item has a Sort Key attribute, the DynamoDB Item Base Context MUST contain:
//# - the key "aws-crypto-sort-name" with a value equal to the [DynamoDB Sort Key Name](./ddb-table-encryption-config.md#dynamodb-sort-key-name).
//# - the [value](#base-context-value-version-1) of the Sort Key.
ensures ret.Success? && config.sortKeyName.Some? ==>
&& config.sortKeyName.value in item
&& SORT_NAME in ret.value
&& DDBEncode(config.sortKeyName.value).Success?
&& var sortName := DDBEncode(config.sortKeyName.value).value;
&& ret.value[SORT_NAME] == sortName
&& EncodeName(config.sortKeyName.value).Success?
&& var sortKeyName : ValidUTF8Bytes := EncodeName(config.sortKeyName.value).value;
&& sortKeyName in ret.value
&& var sortKeyValue : ValidUTF8Bytes := SE.EncodeTerminal(item[config.sortKeyName.value]);
&& ret.value[sortKeyName] == sortKeyValue
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context-version-1
//= type=implication
//# If this item does not have a sort key attribute,
//# the DynamoDB Item Context MUST NOT contain the key `aws-crypto-sort-name`.
ensures ret.Success? && config.sortKeyName.None? ==>
SORT_NAME !in ret.value
{
UTF8.EncodeAsciiUnique();
:- Need(config.partitionKeyName in item, DDBError("Partition key " + config.partitionKeyName + " not found in Item to be encrypted or decrypted"));
var logicalTableName : ValidUTF8Bytes :- DDBEncode(config.logicalTableName);
var partitionName : ValidUTF8Bytes :- DDBEncode(config.partitionKeyName);
var partitionKeyName : ValidUTF8Bytes :- EncodeName(config.partitionKeyName);
var partitionKeyValue : ValidUTF8Bytes := SE.EncodeTerminal(item[config.partitionKeyName]);
if (config.sortKeyName.None?) then
:- Need(|{TABLE_NAME, PARTITION_NAME, SORT_NAME, partitionKeyName}| == 4, E("Internal Error"));
var ec : CMP.EncryptionContext :=
map[
TABLE_NAME := logicalTableName,
PARTITION_NAME := partitionName,
partitionKeyName := partitionKeyValue
];
assert TABLE_NAME in ec;
assert PARTITION_NAME in ec;
assert partitionKeyName in ec;
assert SORT_NAME !in ec;
assert ec[TABLE_NAME] == logicalTableName;
assert ec[PARTITION_NAME] == partitionName;
assert ec[partitionKeyName] == partitionKeyValue;
Success(ec)
else
:- Need(config.sortKeyName.value in item, DDBError("Sort key " + config.sortKeyName.value + " not found in Item to be encrypted or decrypted"));
var sortName :- DDBEncode(config.sortKeyName.value);
var sortKeyName : ValidUTF8Bytes :- EncodeName(config.sortKeyName.value);
var sortKeyValue : ValidUTF8Bytes := SE.EncodeTerminal(item[config.sortKeyName.value]);
:- Need(|{TABLE_NAME, PARTITION_NAME, partitionKeyName, SORT_NAME, sortKeyName}| == 5, E("Internal Error"));
var ec : CMP.EncryptionContext :=
map[
TABLE_NAME := logicalTableName,
PARTITION_NAME := partitionName,
partitionKeyName := partitionKeyValue,
SORT_NAME := sortName,
sortKeyName := sortKeyValue
];
assert TABLE_NAME in ec;
assert PARTITION_NAME in ec;
assert partitionKeyName in ec;
assert SORT_NAME in ec;
assert sortKeyName in ec;
assert ec[TABLE_NAME] == logicalTableName;
assert ec[PARTITION_NAME] == partitionName;
assert ec[partitionKeyName] == partitionKeyValue;
assert ec[SORT_NAME] == sortName;
assert ec[sortKeyName] == sortKeyValue;
Success(ec)
}
function method {:opaque} {:vcs_split_on_every_assert} MakeEncryptionContextV2(
config : InternalConfig,
item : DynamoToStruct.TerminalDataMap)
: (ret : Result<CMP.EncryptionContext, Error>)
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context-version-2
//= type=implication
//# The DynamoDB Item Base Context MUST contain:
//# - the key "aws-crypto-table-name" with a value equal to the DynamoDB Table Name of the DynamoDB Table
//# this item is stored in (or will be stored in).
//# - the key "aws-crypto-partition-name" with a value equal to the name of the Partition Key on this item.
ensures ret.Success? ==>
&& config.partitionKeyName in item
&& TABLE_NAME in ret.value
&& DDBEncode(config.logicalTableName).Success?
&& var logicalTableName : ValidUTF8Bytes := DDBEncode(config.logicalTableName).value;
&& ret.value[TABLE_NAME] == logicalTableName
&& PARTITION_NAME in ret.value
&& DDBEncode(config.partitionKeyName).Success?
&& var partitionName : ValidUTF8Bytes := DDBEncode(config.partitionKeyName).value;
&& ret.value[PARTITION_NAME] == partitionName
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context-version-2
//= type=implication
//# If this item has a Sort Key attribute, the DynamoDB Item Base Context MUST contain:
//# - the key "aws-crypto-sort-name" with a value equal to the [DynamoDB Sort Key Name](./ddb-table-encryption-config.md#dynamodb-sort-key-name).
ensures ret.Success? && config.sortKeyName.Some? ==>
&& config.sortKeyName.value in item
&& SORT_NAME in ret.value
&& DDBEncode(config.sortKeyName.value).Success?
&& var sortName := DDBEncode(config.sortKeyName.value).value;
&& ret.value[SORT_NAME] == sortName
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item-base-context-version-2
//= type=implication
//# If this item does not have a sort key attribute,
//# the DynamoDB Item Context MUST NOT contain the key `aws-crypto-sort-name`.
ensures ret.Success? && config.sortKeyName.None? ==>
SORT_NAME !in ret.value
{
UTF8.EncodeAsciiUnique();
:- Need(config.partitionKeyName in item, DDBError("Partition key " + config.partitionKeyName + " not found in Item to be encrypted or decrypted"));
var logicalTableName : ValidUTF8Bytes :- DDBEncode(config.logicalTableName);
var partitionName : ValidUTF8Bytes :- DDBEncode(config.partitionKeyName);
var partitionKeyName : ValidUTF8Bytes :- EncodeName(config.partitionKeyName);
if (config.sortKeyName.None?) then
assert |{TABLE_NAME, PARTITION_NAME, SORT_NAME}| == 3;
var ec : CMP.EncryptionContext :=
map[
TABLE_NAME := logicalTableName,
PARTITION_NAME := partitionName
];
assert TABLE_NAME in ec;
assert PARTITION_NAME in ec;
assert SORT_NAME !in ec;
assert ec[TABLE_NAME] == logicalTableName;
assert ec[PARTITION_NAME] == partitionName;
Success(ec)
else
:- Need(config.sortKeyName.value in item, DDBError("Sort key " + config.sortKeyName.value + " not found in Item to be encrypted or decrypted"));
var sortName :- DDBEncode(config.sortKeyName.value);
var sortKeyName : ValidUTF8Bytes :- EncodeName(config.sortKeyName.value);
assert |{TABLE_NAME, PARTITION_NAME, SORT_NAME}| == 3;
var ec : CMP.EncryptionContext :=
map[
TABLE_NAME := logicalTableName,
PARTITION_NAME := partitionName,
SORT_NAME := sortName
];
assert TABLE_NAME in ec;
assert PARTITION_NAME in ec;
assert SORT_NAME in ec;
assert ec[TABLE_NAME] == logicalTableName;
assert ec[PARTITION_NAME] == partitionName;
assert ec[SORT_NAME] == sortName;
Success(ec)
}
// string to Error
function method DDBError(s : string) : Error {
Error.DynamoDbItemEncryptorException(message := s)
}
// UTF8.Encode, but return Error
function method DDBEncode(s : string) : Result<UTF8.ValidUTF8Bytes, Error>
{
UTF8.Encode(s).MapFailure(e => DDBError(e))
}
predicate method IsVersion2Schema(actions : DDBE.AttributeActions)
{
exists x <- actions :: actions[x] == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT
}
function method VersionFromActions(actions : DDBE.AttributeActions) : (ret : StructuredEncryptionHeader.Version)
//= specification/dynamodb-encryption-client/ddb-table-encryption-config.md#configuration-version
//= type=implication
//# If any of the [Attribute Actions](#attribute-actions) are configured as
//# [SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT](../structured-encryption/structures.md#contextandsign)
//# then the configuration version MUST be 2; otherwise,
//# the configuration version MUST be 1.
ensures (exists x <- actions :: actions[x] == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT) <==> ret == 2
ensures !(exists x <- actions :: actions[x] == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT) <==> ret == 1
{
if IsVersion2Schema(actions) then
2
else
1
}
function method KeyActionFromVersion(version : StructuredEncryptionHeader.Version) : (ret : CSE.CryptoAction)
//= specification/dynamodb-encryption-client/ddb-table-encryption-config.md#key-action
//= type=implication
//# if the [configuration version](#configuration-version) is 2, then
//# the key action MUST be [SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT](../structured-encryption/structures.md#contextandsign);
//# otherwise, the key action MUST be [SIGN_ONLY](../structured-encryption/structures.md#signonly).
ensures version == 1 <==> ret == CSE.SIGN_ONLY
ensures version == 2 <==> ret == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT
{
if version == 2 then
CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT
else
CSE.SIGN_ONLY
}
function method KeyActionStringFromVersion(version : StructuredEncryptionHeader.Version) : string
{
if version == 2 then
"SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT"
else
"SIGN_ONLY"
}
predicate ValidInternalConfig?(config: InternalConfig)
{
&& config.cmm.ValidState()
&& config.cmpClient.ValidState()
&& config.cmm.Modifies !! {config.cmpClient.History}
&& config.structuredEncryption.ValidState()
&& (config.cmm.Modifies !! config.structuredEncryption.Modifies)
// The partition key MUST be CSE.SIGN_ONLY
&& config.partitionKeyName in config.attributeActionsOnEncrypt
&& config.attributeActionsOnEncrypt[config.partitionKeyName] == KeyActionFromVersion(config.version)
// The sort key MUST be CSE.SIGN_ONLY
&& (config.sortKeyName.Some? ==>
&& config.sortKeyName.value in config.attributeActionsOnEncrypt
&& config.attributeActionsOnEncrypt[config.sortKeyName.value] == KeyActionFromVersion(config.version))
// attributeActionsOnEncrypt only apply on Encrypt.
// The config on Encrypt MAY NOT be the same as the config on Decrypt.
// This means that Encrypt MUST be "forward compatible" with Decrypt.
// Every current and *past* CSE.DO_NOTHING action
// MUST be derivable from allowedUnsigned information
// otherwise Decrypt will attempt to authenticate an attribute that was unauthenticated on Encrypt.
// Also, every current and *past* CSE.ENCRYPT_AND_SIGN or CSE.SIGN_ONLY action
// MUST NOT overlap with allowedUnsigned information
// otherwise Decrypt will not authenticate at attribute that was authenticate on Encrypt.
// For this to work the scope of allowedUnsigned information MUST only increase.
// This means that an attribute that is added to allowedUnsignedAttributes
// MUST NOT ever be removed.
// This means that is a allowedUnsignedAttributePrefix is added
// allowedUnsignedAttributePrefix <= old(allowedUnsignedAttributePrefix).
// The simple case is do not change allowedUnsignedAttributePrefix.
// But allowedUnsignedAttributePrefix MAY get shorter,
// however this is a dangerous operation as it may impact other attributes.
//= specification/dynamodb-encryption-client/decrypt-item.md#signature-scope
//# If an Authenticate Action other than DO_NOTHING is configured for an attribute name included in [Unauthenticated Attributes](./ddb-table-encryption-config.md#unauthenticated-attributes)
//# or beginning with the prefix specified in [Unauthenticated Attribute Prefix](./ddb-table-encryption-config.md#unauthenticated-attribute-prefix),
//# this operation MUST yield an error.
&& (forall attribute <- config.attributeActionsOnEncrypt.Keys
:: ForwardCompatibleAttributeAction(
attribute,
config.attributeActionsOnEncrypt[attribute],
config.allowedUnsignedAttributes,
config.allowedUnsignedAttributePrefix))
// It is forbidden to explicitly configure an attribute with the reserved prefix
&& (forall attribute <- config.attributeActionsOnEncrypt.Keys ::
!(ReservedPrefix <= attribute))
&& (config.internalLegacyOverride.Some? ==> config.plaintextOverride.FORBID_PLAINTEXT_WRITE_FORBID_PLAINTEXT_READ?)
&& (
(|| config.plaintextOverride.FORBID_PLAINTEXT_WRITE_ALLOW_PLAINTEXT_READ?
|| config.plaintextOverride.FORCE_PLAINTEXT_WRITE_ALLOW_PLAINTEXT_READ?)
==>
config.internalLegacyOverride.None?)
}
function ModifiesInternalConfig(config: InternalConfig) : set<object>
{
config.cmm.Modifies
+ config.structuredEncryption.Modifies
+ config.cmpClient.Modifies
}
// return proper Crypto Action by name
function method GetCryptoSchemaActionInner(
config : InternalConfig,
attr : ComAmazonawsDynamodbTypes.AttributeName)
: (ret : Result<CSE.CryptoAction, string>)
ensures (attr !in config.attributeActionsOnEncrypt && InSignatureScope(config, attr)) ==> ret.Failure?
{
if attr in config.attributeActionsOnEncrypt then
Success(config.attributeActionsOnEncrypt[attr])
else if !InSignatureScope(config, attr) then
Success(CSE.CryptoAction.DO_NOTHING)
else
Failure("No Crypto Action configured for attribute " + attr)
}
// get Crypto Action and wrap in CryptoSchema
function method GetCryptoSchemaAction(
config : InternalConfig,
attr : ComAmazonawsDynamodbTypes.AttributeName)
: (ret : Result<CSE.CryptoAction, string>)
ensures (attr !in config.attributeActionsOnEncrypt && InSignatureScope(config, attr)) ==> ret.Failure?
{
GetCryptoSchemaActionInner(config, attr)
}
// return proper Authenticate Action by name
function method GetAuthenticateSchemaAction(
config : InternalConfig,
attr : ComAmazonawsDynamodbTypes.AttributeName)
: (ret : CSE.AuthenticateAction)
requires ValidInternalConfig?(config)
//= specification/dynamodb-encryption-client/decrypt-item.md#signature-scope
//= type=implication
//# An Attribute on a DynamoDB Item MUST NOT be considered as within the signature scope
//# if it's Attribute Name is included in [Unauthenticated Attributes](./ddb-table-encryption-config.md#unauthenticated-attributes)
//# or if it's Attribute Name begins with the prefix specified in
//# [Unauthenticated Attribute Prefix](./ddb-table-encryption-config.md#unauthenticated-attribute-prefix).
//= specification/dynamodb-encryption-client/decrypt-item.md#signature-scope
//= type=implication
//# Otherwise, Attributes MUST be considered as within the signature scope.
ensures (ret == CSE.DO_NOT_SIGN) <==> !InSignatureScope(config, attr)
{
if InSignatureScope(config, attr) then
CSE.SIGN
else
CSE.DO_NOT_SIGN
}
// get CryptoSchema for this item
function method ConfigToCryptoSchema(
config : InternalConfig,
item : ComAmazonawsDynamodbTypes.AttributeMap)
: (ret : Result<CSE.CryptoSchemaMap, DDBE.Error>)
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# The [Attributes Actions](./ddb-table-encryption-config.md#attribute-actions)
//# configured on this Item Encryptor MUST specify a Crypto Action
//# for every attribute in the [input DynamoDB Item](#dynamodb-item)
//# (Attribute Actions MAY specify a Crypto Action for an attribute not
//# in the input DynamoDB Item).
ensures forall k <- item.Keys ::
(k !in config.attributeActionsOnEncrypt && InSignatureScope(config, k)) ==> ret.Failure?
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# - The Crypto Schema MUST NOT contain more Crypto Actions than those specified by the previous point.
ensures ret.Success? ==> item.Keys == ret.value.Keys
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# - For every attribute on the input Item,
//# there MUST exist a Crypto Action in the Crypto Schema
//# such that the Crypto Action indexed by that attribute name in the Crypto Schema
//# equals the Crypto Action indexed by that attribute name in the configured Attribute Actions.
ensures ret.Success? ==> forall k <-item.Keys ::
&& GetCryptoSchemaAction(config, k).Success?
&& ret.value[k] == GetCryptoSchemaAction(config, k).value
&& (k in config.attributeActionsOnEncrypt ==>
ret.value[k] == config.attributeActionsOnEncrypt[k])
{
var schema := map k <- item :: k := GetCryptoSchemaAction(config, k);
DynamoToStruct.MapKeysMatchItems(item);
DynamoToStruct.SimplifyMapValueSuccess(schema);
var actionMapRes := DynamoToStruct.SimplifyMapValue(schema);
assert actionMapRes.Failure? ==> exists kv <- item.Items :: GetCryptoSchemaAction(config, kv.0).Failure?;
assert actionMapRes.Failure? <==> exists k <- item.Keys :: schema[k].Failure?;
assert actionMapRes.Failure? <==> exists k <- item.Keys :: GetCryptoSchemaAction(config, k).Failure?;
DynamoToStruct.MapError(actionMapRes)
}
// get AuthenticateSchema for this item
function method ConfigToAuthenticateSchema(
config : InternalConfig,
item : ComAmazonawsDynamodbTypes.AttributeMap)
: (ret : CSE.AuthenticateSchemaMap)
requires ValidInternalConfig?(config)
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# - The number of Authenticate Actions in the Authenticate Schema
//# MUST EQUAL the number of Attributes on the [input DynamoDB Item](#input-dynamodb-item).
ensures item.Keys == ret.Keys
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# - For every Attribute in the [input DynamoDB Item](#input-dynamodb-item)
//# that is not in the [signature scope](#signature-scope),
//# there MUST exist a [DO_NOT_SIGN Authenticate Action](../structured-encryption/structures.md#do_not_sign)
//# in the Authenticate Schema,
//# string indexed at the top level by that attribute name.
ensures forall k <-item.Keys :: !InSignatureScope(config, k) ==> ret[k] == CSE.DO_NOT_SIGN
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# - For every Attribute in the [input DynamoDB Item](#input-dynamodb-item)
//# that is in the [signature scope](#signature-scope),
//# there MUST exist a [SIGN Authenticate Action](../structured-encryption/structures.md#sign)
//# in the Authenticate Schema,
//# string indexed at the top level by that attribute name.
ensures forall k <-item.Keys :: InSignatureScope(config, k) ==> ret[k] == CSE.SIGN
{
map k <- item | true :: k := GetAuthenticateSchemaAction(config, k)
}
//= specification/dynamodb-encryption-client/decrypt-item.md#determining-plaintext-items
//= type=implication
//# An item MUST be determined to be plaintext if it does not contain
//# attributes with the names "aws_dbe_head" and "aws_dbe_foot".
predicate method IsPlaintextItem(ddbItem: ComAmazonawsDynamodbTypes.AttributeMap) {
&& SE.HeaderField !in ddbItem
&& SE.FooterField !in ddbItem
}
function method ConvertCryptoSchemaToAttributeActions(config: ValidConfig, schema: CSE.CryptoSchemaMap)
: (ret: Result<map<ComAmazonawsDynamodbTypes.AttributeName, CSE.CryptoAction>, Error>)
requires forall k <- schema :: SE.IsAuthAttr(schema[k])
ensures ret.Success? ==> forall k <- ret.value.Keys :: InSignatureScope(config, k)
ensures ret.Success? ==> forall k <- ret.value.Keys :: !ret.value[k].DO_NOTHING?
{
:- Need(forall k <- schema :: InSignatureScope(config, k),
DynamoDbItemEncryptorException( message := "Received unexpected Crypto Schema: mismatch with signature scope"));
:- Need(forall k <- schema :: ComAmazonawsDynamodbTypes.IsValid_AttributeName(k),
DynamoDbItemEncryptorException( message := "Received unexpected Crypto Schema: Invalid attribute names"));
Success(schema)
}
predicate EncryptItemEnsuresPublicly(input: EncryptItemInput, output: Result<EncryptItemOutput, Error>)
{true}
function method GetItemNames(item : ComAmazonawsDynamodbTypes.AttributeMap) : string
{
// We happen to order these values, but this ordering MUST NOT be relied upon.
var keys := SortedSets.ComputeSetToOrderedSequence2(item.Keys, CharLess);
if |keys| == 0 then
"item is empty"
else
Join(keys, " ")
}
function method KeyMissingMsg(
config: InternalConfig,
item : ComAmazonawsDynamodbTypes.AttributeMap,
tag : string)
: string
{
"On " + tag + " : "
+
(if config.partitionKeyName !in item then
"Partition key '" + config.partitionKeyName + "' does not exist in item. "
else
"")
+
(if config.sortKeyName.Some? && config.sortKeyName.value !in item then
"Sort key '" + config.sortKeyName.value + "' does not exist in item. "
else
"")
+ "Item contains these attributes : "
+ GetItemNames(item) + "."
}
predicate method ContextAttrsExist(actions : DDBE.AttributeActions, item : DDB.AttributeMap)
{
forall k <- actions :: (actions[k] == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT) ==> (k in item)
}
function method ContextMissingMsg(actions : DDBE.AttributeActions, item : DDB.AttributeMap) : string
{
var s := set k <- actions |
&& actions[k] == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT
&& k !in item;
var missing := SortedSets.ComputeSetToOrderedSequence2(s, CharLess);
if |missing| == 0 then
"No missing SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT attributes."
else if |missing| == 1 then
"Attribute " + missing[0] + " was configured with SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT but was not present in item to be encrypted."
else
"These attributes were configured with SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT but were not present in item to be encrypted."
+ Join(missing, ",")
}
// public Encrypt method
method {:vcs_split_on_every_assert} EncryptItem(config: InternalConfig, input: EncryptItemInput)
returns (output: Result<EncryptItemOutput, Error>)
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item
//= type=implication
//# This item MUST include an Attribute with a name that matches the
//# [DynamoDB Partition Key Name](./ddb-table-encryption-config.md#dynamodb-partition-key-name)
//# configured on the [DynamoDB Item Encryptor](./ddb-item-encryptor.md).
ensures output.Success? ==> config.partitionKeyName in input.plaintextItem
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item
//= type=implication
//# Otherwise this operation MUST yield an error.
ensures config.partitionKeyName !in input.plaintextItem ==> output.Failure?
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item
//= type=implication
//# If the [DynamoDB Item Encryptor](./ddb-item-encryptor.md)
//# has a [DynamoDB Sort Key Name](./ddb-table-encryption-config.md#dynamodb-sort-key-name) configured,
//# this item MUST include an Attribute with that name.
ensures output.Success? ==> (config.sortKeyName.None? || config.sortKeyName.value in input.plaintextItem)
// Otherwise this operation MUST yield an error.
ensures config.sortKeyName.Some? && config.sortKeyName.value !in input.plaintextItem ==> output.Failure?
//= specification/dynamodb-encryption-client/encrypt-item.md#dynamodb-item
//= type=implication
//# If the [DynamoDB Item Encryptor](./ddb-item-encryptor.md)
//# has any attribute configured as
//# [SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT](../structured-encryption/structures.md#contextandsign)
//# then this item MUST include an Attribute with that name.
ensures output.Success? ==>
forall k <- config.attributeActionsOnEncrypt :: (config.attributeActionsOnEncrypt[k] == CSE.SIGN_AND_INCLUDE_IN_ENCRYPTION_CONTEXT) ==> (k in input.plaintextItem)
// ContextAttrsExist(config.attributeActionsOnEncrypt, input.plaintextItem)
ensures
&& output.Success?
&& !(config.internalLegacyOverride.Some? && config.internalLegacyOverride.value.policy.FORCE_LEGACY_ENCRYPT_ALLOW_LEGACY_DECRYPT?)
&& !(config.plaintextOverride.FORCE_PLAINTEXT_WRITE_ALLOW_PLAINTEXT_READ?)
==>
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# Given the converted [Structured Data](../structured-encryption/structures.md#structured-data),
//# this operation MUST delegate encryption of this data to
//# Structured Encryption Client's [Encrypt Structure](../structured-encryption/encrypt-structure.md),
//# with the following inputs:
&& (|config.structuredEncryption.History.EncryptStructure| == |old(config.structuredEncryption.History.EncryptStructure)| + 1)
&& (Seq.Last(config.structuredEncryption.History.EncryptStructure).output.Success?)
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# - Crypto Schema MUST be a [Crypto Schema](../structured-encryption/structures.md#crypto-schema)
//# analogous to the [configured Attribute Actions](./ddb-table-encryption-config.md#attribute-actions).
&& ConfigToCryptoSchema(config, input.plaintextItem).Success?
&& Seq.Last(config.structuredEncryption.History.EncryptStructure).input.cryptoSchema
== ConfigToCryptoSchema(config, input.plaintextItem).value
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# - Structured Data MUST be the Structured Data converted above.
&& DynamoToStruct.ItemToStructured(input.plaintextItem).Success?
&& var plaintextStructure := DynamoToStruct.ItemToStructured(input.plaintextItem).value;
&& Seq.Last(config.structuredEncryption.History.EncryptStructure).input.plaintextStructure
== plaintextStructure
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# - Encryption Context MUST be this input Item's [DynamoDB Item Base Context](#dynamodb-item-base-context).
&& MakeEncryptionContextForEncrypt(config, plaintextStructure).Success?
&& Seq.Last(config.structuredEncryption.History.EncryptStructure).input.encryptionContext
== Some(MakeEncryptionContextForEncrypt(config, plaintextStructure).value)
&& output.value.parsedHeader.Some?
&& var structuredEncOut := Seq.Last(config.structuredEncryption.History.EncryptStructure).output.value;
&& var parsedHeaderMap := structuredEncOut.cryptoSchema;
&& (forall k <- parsedHeaderMap ::
&& SE.IsAuthAttr(parsedHeaderMap[k]))
&& var maybeCryptoSchema := ConvertCryptoSchemaToAttributeActions(config, structuredEncOut.cryptoSchema);
&& maybeCryptoSchema.Success?
&& ConvertContextForSelector(structuredEncOut.parsedHeader.encryptionContext).Success?
&& var selectorContext := ConvertContextForSelector(structuredEncOut.parsedHeader.encryptionContext).value;
&& output.value.parsedHeader.value == ParsedHeader(
attributeActionsOnEncrypt := maybeCryptoSchema.value,
algorithmSuiteId := structuredEncOut.parsedHeader.algorithmSuiteId,
storedEncryptionContext := structuredEncOut.parsedHeader.storedEncryptionContext,
encryptedDataKeys := structuredEncOut.parsedHeader.encryptedDataKeys,
encryptionContext := structuredEncOut.parsedHeader.encryptionContext,
selectorContext := selectorContext
)
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//= type=implication
//# If a [Plaintext Policy](./ddb-table-encryption-config.md#plaintext-policy) of
//# `FORCE_PLAINTEXT_WRITE_ALLOW_PLAINTEXT_READ` is specified,
//# this operation MUST NOT encrypt the input item,
//# and MUST passthrough that item as the output.
ensures
&& config.plaintextOverride.FORCE_PLAINTEXT_WRITE_ALLOW_PLAINTEXT_READ?
&& output.Success?
==>
&& output.value.encryptedItem == input.plaintextItem
&& output.value.parsedHeader == None
ensures output.Success? ==> |input.plaintextItem| <= MAX_ATTRIBUTE_COUNT
{
:- Need(
&& config.partitionKeyName in input.plaintextItem
&& (config.sortKeyName.None? || config.sortKeyName.value in input.plaintextItem)
, E(KeyMissingMsg(config, input.plaintextItem, "Encrypt")));
:- Need(ContextAttrsExist(config.attributeActionsOnEncrypt, input.plaintextItem),
E(ContextMissingMsg(config.attributeActionsOnEncrypt, input.plaintextItem)));
if |input.plaintextItem| > MAX_ATTRIBUTE_COUNT {
var actCount := String.Base10Int2String(|input.plaintextItem|);
var maxCount := String.Base10Int2String(MAX_ATTRIBUTE_COUNT);
return Failure(E("Item to encrypt had " + actCount + " attributes, but maximum allowed is " + maxCount));
}
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//# If a [Legacy Policy](./ddb-table-encryption-config.md#legacy-policy) of
//# `FORCE_LEGACY_ENCRYPT_ALLOW_LEGACY_DECRYPT` is specified,
//# this operation MUST delegate encryption of this item to the
//# [Legacy Encryptor](./ddb-table-encryption-config.md#legacy-encryptor),
//# using the configured [Attribute Flags](./ddb-table-encryption-config.md) as input.
if config.internalLegacyOverride.Some? && config.internalLegacyOverride.value.policy.FORCE_LEGACY_ENCRYPT_ALLOW_LEGACY_DECRYPT? {
var encryptItemOutput :- config.internalLegacyOverride.value.EncryptItem(input);
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//# The item returned by this operation MUST be the item outputted by the
//# [Legacy Encryptor](./ddb-table-encryption-config.md#legacy-encryptor).
return Success(encryptItemOutput);
}
if (config.plaintextOverride.FORCE_PLAINTEXT_WRITE_ALLOW_PLAINTEXT_READ?) {
var passthroughOutput := EncryptItemOutput(
encryptedItem := input.plaintextItem,
parsedHeader := None
);
return Success(passthroughOutput);
}
var plaintextStructure :- DynamoToStruct.ItemToStructured(input.plaintextItem)
.MapFailure(e => Error.AwsCryptographyDbEncryptionSdkDynamoDb(e));
var context :- MakeEncryptionContextForEncrypt(config, plaintextStructure);
var cryptoSchema :- ConfigToCryptoSchema(config, input.plaintextItem)
.MapFailure(e => Error.AwsCryptographyDbEncryptionSdkDynamoDb(e));
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//# This operation MUST create a
//# [Required Encryption Context CMM](https://github.com/awslabs/private-aws-encryption-sdk-specification-staging/blob/dafny-verified/framework/required-encryption-context-cmm.md)
//# with the following inputs:
//# - This item encryptor's [CMM](./ddb-table-encryption-config.md#cmm) as the underlying CMM.
//# - The keys from the [DynamoDB Item Base Context](#dynamodb-item-base-context)
var contextKeysX : seq<seq<uint8>> := SortedSets.ComputeSetToOrderedSequence2(context.Keys, ByteLess);
assert forall k <- contextKeysX :: ValidUTF8Seq(k) by {
assert forall k <- contextKeysX :: k in context.Keys;
assert forall k <- context.Keys :: ValidUTF8Seq(k);
}
var contextKeys : seq<CMP.Utf8Bytes> := contextKeysX;
var reqCMMR := config.cmpClient.CreateRequiredEncryptionContextCMM(
CMP.CreateRequiredEncryptionContextCMMInput(
underlyingCMM := Some(config.cmm),
keyring := None,
requiredEncryptionContextKeys := contextKeys
)
);
var reqCMM :- reqCMMR.MapFailure(e => AwsCryptographyMaterialProviders(e));
var encryptRes := config.structuredEncryption.EncryptStructure(
CSE.EncryptStructureInput(
tableName := config.logicalTableName,
plaintextStructure:=plaintextStructure,
cryptoSchema:=cryptoSchema,
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//# - The CMM MUST be the CMM created above.
cmm:= reqCMM,
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//# - If configured, the Algorithm Suite MUST be the
//# [Algorithm Suite configured on this Item Encryptor](./ddb-table-encryption-config.md#algorithm-suite).
//= specification/dynamodb-encryption-client/encrypt-item.md#behavior
//# If not configured on the Item Encryptor, Algorithm Suite MUST NOT be specified.
// If not specified on input, the algorithm suite exists as None on the config
algorithmSuiteId:=config.algorithmSuiteId,
encryptionContext:=Some(context)
)
);
assert {:split_here} true;
var encryptVal :- encryptRes.MapFailure(
e => Error.AwsCryptographyDbEncryptionSdkDynamoDb(DDBE.AwsCryptographyDbEncryptionSdkStructuredEncryption(e)));
var encryptedData := encryptVal.encryptedStructure;
:- Need(forall k <- encryptedData :: DDB.IsValid_AttributeName(k), E(""));
var ddbKey :- DynamoToStruct.StructuredToItem(encryptedData)
.MapFailure(e => Error.AwsCryptographyDbEncryptionSdkDynamoDb(e));
var parsedActions :- ConvertCryptoSchemaToAttributeActions(config, encryptVal.cryptoSchema);
var selectorContextR := ConvertContextForSelector(encryptVal.parsedHeader.encryptionContext);
var selectorContext :- selectorContextR.MapFailure(e => E(e));
var parsedHeader := ParsedHeader(
attributeActionsOnEncrypt := parsedActions,
algorithmSuiteId := encryptVal.parsedHeader.algorithmSuiteId,
storedEncryptionContext := encryptVal.parsedHeader.storedEncryptionContext,
encryptedDataKeys := encryptVal.parsedHeader.encryptedDataKeys,
encryptionContext := encryptVal.parsedHeader.encryptionContext,
selectorContext := selectorContext
);
output := Success(EncryptItemOutput(
encryptedItem := ddbKey,
parsedHeader := Some(parsedHeader)
));
}
predicate DecryptItemEnsuresPublicly(input: DecryptItemInput, output: Result<DecryptItemOutput, Error>)
{true}
// public Decrypt method
method {:vcs_split_on_every_assert} DecryptItem(config: InternalConfig, input: DecryptItemInput)
returns (output: Result<DecryptItemOutput, Error>)
//= specification/dynamodb-encryption-client/decrypt-item.md#input-dynamodb-item
//= type=implication
//# This item MUST include an Attribute with a name that matches the
//# [DynamoDB Partition Key Name](./ddb-table-encryption-config.md#dynamodb-partition-key-name)
//# configured on the [DynamoDB Item Encryptor](./ddb-item-encryptor.md).
ensures output.Success? ==> config.partitionKeyName in input.encryptedItem
//= specification/dynamodb-encryption-client/decrypt-item.md#input-dynamodb-item
//= type=implication
//# Otherwise this operation MUST yield an error.
ensures config.partitionKeyName !in input.encryptedItem ==> output.Failure?
//= specification/dynamodb-encryption-client/decrypt-item.md#input-dynamodb-item
//= type=implication
//# If the [DynamoDB Item Encryptor](./ddb-item-encryptor.md)
//# has a [DynamoDB Sort Key Name](./ddb-table-encryption-config.md#dynamodb-sort-key-name) configured,
//# this item MUST include an Attribute with that name.
ensures output.Success? ==> config.sortKeyName.None? || config.sortKeyName.value in input.encryptedItem
// Otherwise this operation MUST yield an error.
ensures config.sortKeyName.Some? && config.sortKeyName.value !in input.encryptedItem ==> output.Failure?
ensures
&& output.Success?
&& !(config.internalLegacyOverride.Some? && config.internalLegacyOverride.value.IsLegacyInput(input))
&& (config.plaintextOverride.FORBID_PLAINTEXT_WRITE_FORBID_PLAINTEXT_READ? || !IsPlaintextItem(input.encryptedItem))
==>
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# Given the converted [Structured Data](../structured-encryption/structures.md#structured-data),
//# this operation MUST delegate decryption of this data to
//# Structured Encryption Client's [Decrypt Structure](../structured-encryption/encrypt-structure.md),
//# with the following inputs:
&& (|config.structuredEncryption.History.DecryptStructure| == |old(config.structuredEncryption.History.DecryptStructure)| + 1)
&& (Seq.Last(config.structuredEncryption.History.DecryptStructure).output.Success?)
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# - Authenticate Schema MUST be a [Authenticate Schema](../structured-encryption/structures.md#crypto-schema)
//# built with the following requirements:
&& Seq.Last(config.structuredEncryption.History.DecryptStructure).input.authenticateSchema
== ConfigToAuthenticateSchema(config, input.encryptedItem)
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# - Encrypted Structured Data MUST be the Structured Data converted above.
&& DynamoToStruct.ItemToStructured(input.encryptedItem).Success?
&& var plaintextStructure := DynamoToStruct.ItemToStructured(input.encryptedItem).value;
&& Seq.Last(config.structuredEncryption.History.DecryptStructure).input.encryptedStructure
== plaintextStructure
//= specification/dynamodb-encryption-client/decrypt-item.md#dynamodb-item-base-context
//= type=implication
//# The item to be encrypted MUST have an attribute named `aws_dbe_head`.
&& SE.HeaderField in input.encryptedItem
&& var header := input.encryptedItem[SE.HeaderField];
//= specification/dynamodb-encryption-client/decrypt-item.md#dynamodb-item-base-context
//= type=implication
//# The attribute named `aws_dbe_head` MUST be of type `B` Binary.
&& header.B?
&& 0 < |header.B|
//= specification/dynamodb-encryption-client/decrypt-item.md#behavior
//= type=implication
//# - Encryption Context MUST be the input Item's [DynamoDB Item Base Context](./encrypt-item.md#dynamodb-item-base-context).
&& MakeEncryptionContextForDecrypt(config, header.B, plaintextStructure).Success?
&& Seq.Last(config.structuredEncryption.History.DecryptStructure).input.encryptionContext
== Some(MakeEncryptionContextForDecrypt(config, header.B, plaintextStructure).value)
//= specification/dynamodb-encryption-client/decrypt-item.md#output
//= type=implication
//# This operation MUST also output a [Parsed Header](#parsed-header) if the following is true:
//# - The operation is not using a [Legacy Policy](./ddb-table-encryption-config.md#legacy-policy) that allows legacy decrypts,
//# and the input item is a [legacy item](#determining-legacy-items).
//# - The operation is not using a [Plaintext Policy](./ddb-table-encryption-config.md#plaintext-policy) that allows plaintext reads,